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?