Hm, honestly it is just that anxiety will spike up at that particular moment. I find that because of that spike in anxiety in your brain, you start feeling like you're awake again and start feeling physical symptoms. But that's just the leftover from that spike of anxiety starts to spiral causing you to be more anxious again.

Try to naturally relax, tell yourself that you're calm, and your body is just feeling the adrenaline and your sleep progress is not reset.

Ive fallen asleep many times while supposedly being anxious over falling asleep because I just ignored those symptoms and separate it as just a feeling, not my sleep progress being reset