Blood rushing when transitioning from sleep to being awake

Also, I am 43 years old. This started when I was 35.

I think I need a better understanding of what you are feeling exactly when this starts happening. Where are you when it begins? Are you still in bed lying down or have you gotten up out of bed? I am trying to determine if you are talking about something you feel in your head that you also feel in your body like sleep paralysis or is it something you feel only in your body when getting up out of bed that is linked to perhaps to blood pressure and pulse rate. And then there is so much more than that. I've had both of these things happen to me. So, I would need to know more about what you are feeling exactly and where you are when it happens and how long before it stops.
When I read your post the first thing I thought of because you mentioned your vein, blood, and pulse rhythm was the feeling I get a lot of the time when I first rise out of bed. I feel pressure in my head and in my ears. Sometimes I can hear a switching sound in my ears or hear and feel a buzzing in my ears and body. It is an uncomfortable, unpleasant feeling. My body feels extra heavy, and I feel like I can't catch my breath very well. I have linked some symptoms to my issue of having decreased oxygen whenever my body is in a lying down position. I am supposed to be taking oxygen every night. Not due to Sleep Apnea but just a decreased oxygen level lying down. The doctors don't know why. However, I know when it is due to a lack of oxygen or this other thing that happens to me upon getting out of bed that I just see as normal for me now. And those symptoms are what I wrote above and what I feel most mornings. But you said you are afraid you won't be able to wake up. But since you are able to think that tells me you are awake. Unless, you are referring to something such as sleep Paralysis. I also suffer from this. I had this since I turned 18. I am 48 now. So, I need more information about what is going on with you exactly. There are so many different conditions. Like I said above about how long is it happening for before it completely goes away? And where are you? Are you still lying down but trying to wake up or are you up out of bed trying to wake up?

I am laying down in my bed when this happens, I am in the process of waking up. This is after me sleeping for 8+ hours. I feel very exhausted waking up. So when I am trying to wake up, I feel like a can't. I sorta doze in and out for sometimes up to an hour. I feel this throughout my whole body. My pulse, rushing fast. Shaky feeling. The minute I am completely awake and start moving for the day, I don't have this feeling anymore.

Never thought about low oxygen levels or sleep paralysis. I have done a sleep study but that was back in 2012. Could redo that again as I didn't have sleep apnea then.

How is your sleep? You said you get 8 hours of sleep. Is it good sleep or do you wake up a lot? This is how I get after I haven't been able to sleep more than 3 hours total every night for several weeks to months. I go lay down and try to sleep for 8 hours but I constantly wake up every 45 minutes or so because of my oxygen getting to low I think. My body automatically wakes me up. And then once I am awake, I have anxiety about needing to empty my bladder. So, I then get up. The 3 hours I get is in total. I wake up at least three times in those three hours. When this happens for a long time, I get Narcolepsy type symptoms where I can just fall asleep during the day at any given moment. But I also have that severe grogginess and being out of it upon wakening when I finally get into a deeper sleep toward the morning and my body tries to wake me up. If you look up Narcolepsy, I was surprised to find out that their symptoms is because they constantly wake up during the night and therefore don't get nearly enough sleep as they need and then eventually taking its toll, they begin falling asleep during activities during the day.
It also reminds me of my milder bits of sleep paralysis. Do you try to move your body at all during these times? Are you awake enough to think about trying? I think before you said you try to wake up. If so, can you move your limbs? And during that time are you in and out of dreaming but at the same time you know you are in your bed? Early hour sleep paralysis isn't uncommon for people who have it. Just trying to get more information.

I move a lot when I sleep. My husband even says I talk to him and can sometimes have a whole conversation. But I do not recall any of it, ever. I feel very exhausted when I do wake up. I can even take clothes off if I am to hot and when I wake up, I really don't remember ever waking up to do that. When I am waking up in the morning I go in between dreaming and being awake sometimes. I am so groggy when I am waking up I don't even think about moving. So I don't move anything, I don't think.

This sounds similar to what I've been dealing with for four years.
The "rushes" start around 5 am. Feels like a"wave" of adrenaline and I start to sweat and have weird,sick- feeling dreams as I doze off again.
I think this is related to the "cortisol awakening response", but I also have anxiety. It's a lousy way to start every day, and I wish I had a solution.

I'll look into that. I read about someone saying fight or flight while waking up. I seen a post on here about body vibrations