Sensation of falling or tumbling as sleep comes

Hello! I searched around to see if this may have been covered elsewhere but didn't turn anything up, but apologies if this is in another thread.

For about two weeks now I am able to fall asleep just fine, but if I wake up in the middle of night and then try to get back asleep then just as I begin to sleep I experienced a sensation of falling with some spinning that jerks me awake. This will happen multiple times for up to two hours until I'm able to overcome it and fall asleep for any duration of time. I wondered if it were inner ear and balance related, but it happens no matter what way my body or head are positioned. I do have sciatica and wondered if in some way this is connected, but I'm unsure if there's any correlation.

It's also odd that so far I can get to sleep initially without this happening, but if I get up to urinate, hear a loud sound outside like thunder, or the cat causes trouble, it will happen when attempted to sleep again.

Thanks in advance for any pointers.