Head feels like it will explode daily. Severe cognitive difficulties

I'm so so sorry for what you are going through. I can give you my experiences that may or may not mean anything for you... Maybe you can contact The Hydrocephalus Association. I guess your neurologist didn't see any problem with fluid on your brain. But maybe they know of a specialist in your area that could see you and rule it out for sure.
Now, my experience. I remember the same kind of pain you describe. I had a root canal done on my far back upper tooth. He cleaned out 1 root but left 2 that got infected.. I did not find this. out until years and years of constant sinus infections and migraines. I had a 3D image of the tooth in front of it that needed a root canal, and the dentist was confused why I had a partial root canal that was done and obvious infection in 2 of the 3 roots left. I went back to my dentist who asked if that tooth had direct pain. I said no. And he said it was ok , because that infection would stay in the tooth area and never be a problem... After a year of further migraines and sinus problems that got worse and worse, I decided on my own to try to find a dentist surgeon who could remove that back upper tooth, even though it would effect my bite.
I never expected what would happen. The day I had that tooth removed. I could barely breath out of the right side of my nose for years.... The right side completely cleared. My severe headache was gone. I walked out of the office and my vision was greatly improved. I had worn glasses to drive for over 10 years. I could suddenly read license plates and street signs and didn't need the glasses at all. While the area was still draining this continued. After 4 days the headache returned, but less severe . And over 10 years later , now over 70 yrs old, my vision is starting to blur a bit. Expected with age i guess... But the only headaches I get now I believe are basically triggered by allergies. I can change my diet and they will go away..... Maybe contacting a good allergist could find something too..... sometimes a chiropractor can help if I've overdone yard work etc.
I know how frustrating struggling to find a doctor who wants to keep looking for answers with you. I used to think posting on this Mayo sight might wake up some doctors at Mayo that might read and discover some answers..... But I really don't believe any doctors from Mayo look at this sight... I'm really not sure what it's for. Just frustrated suffering people that get no help from the words MAYO CLINIC.
I'm praying for you. You are so young. I guess I believe in miracles, because that's what I felt when I got a tooth pulled that had been infected over 20 years with No dentist ever noticing. Only a 3D image found it which your regular dentist will never look that deep at your roots.
It could be a simple answer I'm hoping for you. Try to track what you eat. What was going on when it started .. I know over the years things made my headaches worse. Eating Ranch dressing, smelling bleach or eucalyptus. I've always tried to use everything unscented. But I don't have to do that as much anymore.
There's a book called " Is This Your Child" , about things that trigger children's actions. I believe the same kind of things can trigger headaches.... I never found a doctor who actually tried to find a cure for my headaches. Only drugs.... Which somehow I never accepted taking the DAILY meds to prevent migraines. I always said, why take drugs every day, if I go 2 weeks now with no headache. What effect does a daily drug do, if it really doesn't get rid of the headache.... and it never did......
Keep looking for answers. I have found a chiropractic adjustment could make my headaches dramatically better, but you have to be careful, because they have made it dramatically worse too... It has come to a 50/50 on that now... I don't let them adjust my neck because my neck bones are messed up and too fragile for that. but back adjustments do help....
Take care.... please.... I know people around you don't always understand when they are blessed with NO headaches..... please keep looking.... track your food and surroundings maybe....
I quit looking on this sight for years because it never helped. But I'm not sure why I looked today. Maybe a reason? Praying for answers for you.

OH... just to let you know. I was a flight attendant for 30 yrs. There are drugs you can't take and fly.. Headaches and flying was a challenge. Luckily it was a flexible job too. I did find out after taking darvocet for over 5 years ( the only drug available back then for headaches) that it was really making my headaches worse.. a lot worse... at that time I quit taking it because I knew it didn't help. Then is when I realized it made it worse.... The fewer drugs the better..... I cannot take tylenol at all because I took so much for years. Only Advil work now...
I never took antidepresents. Read the side effects of your meds , AND BELIEVE THEM. I know doctors completely ignore side effects. I don't. I know codeine makes my headaches worse, yet a doctor wrote a prescription for cough med with codeine. Track things.... I took imitrex for years. Was a miracle drug, but when generic started, I found I could only take generic from 1 supplier, but 2 others didn't work... I had to stop the imitrex after a couple years because now it causes chest pains.... But Advil seems to be fine for me now.
So sorry if this is too much info........................... years of experience is a lot, but I believe you can find a trigger and never have to have all this EXPERIENCE.....
rooting for you... You WILL find it...... take care........ T

I understand getting an MRI of the spine, but what would an upright MRI achieve?

Do you know what kind of specialist I would need to see for CCI?

I have not had imaging of my neck, but multiple people on this forum have suggested that to me. What might imaging of the neck rule out? A spinal leak? CCI?

Neurosurgeon dx mine

C2 and C3 send nerves to the back of your head. The cervical neck can negatively affect the autonomic nervous system giving you the symptoms of ahedonia etc. https://caringmedical.com/prolotherapy-news/symptoms-dysautonomia/
An upright MRI can give marked view of pressures on the central canal. This might be especially helpful if you don't wake up with the headache.

This article explains how upright MRI can see more details than a flat MRI.
https://neurolaunch.com/upright-brain-mri/

I wake up with the headache. I am wondering if it's better to get an upright MRI or a cervical MRI?

See RFA, "Posted by summerstar @summerstar, Aug 27, 2023" for comparison only. My Cervical radiofrequency ablation (RFA) was mostly successful and did not include any of the problems summerstar experienced.
In my case I suffered with severe pain headaches for decades. Those ongoing and frequent pain headaches subsided after two RFA treatments in 2017. Not sure how much later head pressure became an apparent new side effect. To date headaches with pain have been more of a nuisance, infrequent and tolerable but the head pressure has continued and has gotten progressively worse since my serious bout with West Nile Virus in late 2021. A recent MRI of the brain did not indicate any serious problems other than being 78 but I continue to deal with this intolerable head pressure headaches. I welcome anyone's response.

Sorry, and upright cervical. Some clinics offer seated MRIs of the neck to show the position of everything in the upright position instead of supine.

Getting a referral to a Spine and Pain Doctor would help greatly! They will do all the test needed. Your symptoms sound a lot like mine! I have Occipital Neuropathy and have had all kinds of procedures done such as epidurals and injections that help with the neuropathy and headaches. I am currently getting worked up for a spinal cord stimulator trail. I am praying that this will at least help with the pain enough that I can go swimming a paddleboarding again.
I hope you get some relief soon!
Blessings,