I experienced a thunderclap headache once in my life and take all precautions never to have it again.
Beyond painful, beyond frightening.
I believe the triggers for me was working out much too intensely at the gym (I was hitting a punching bag, great stress reliever), dehydration and fatigue. I was 67 at the time. It came on so suddenly, I thought it was a stroke, I was screaming with pain. 911 called, my blood pressure was what is called "hypertensive crisis" and brought to the ER. The ER staff attempted to give me a "migraine cocktail"...3 drugs, one of which was IV Benadryl. I didn't get to the other 2.
The RN gave this drug via IV much too fast, developed chest pain and almost passed out. All a nightmare, ultimately I was given IV Toradol and Valium. I was discharged with pain but it was doable. However, this episode kicked off 9 months of migraines, believe it or not. Which I have to this day, 4 years later.
I have learned any sudden increase in "head pressure" will start the beginnings of a thunderclap. So I am very careful. I can no longer have organisms, just the start of such, I feel the pressure in back of my head really to explode. So try to identify your triggers, always start hydrated and if you do have hypertension be very careful of a possible increase in your B/P - whatever the cause may be. My CT Scan of the brain was "normal" in the ER. I did not have a stroke but the "thunderclap". Please take care of yourself. Most folks never heard of this headache event...but once it happens to you, you never forget it. Be well.