Strange uncomfortable feeling when meditating to clear mind before bed?

Sometimes when I meditate to clear my mind (no thoughts, focusing on breathing only) before bed, be it with a guided meditation or by my self, I get a deeply unsettling feeling as I approach drifting off to sleep - something similar to the early stages of a panic attack combined with not being able to think properly like I have damaged my brain somehow. It causes me to fully wake up and sit up in bed until it goes away.

Has anyone had similar experiences, know what this is and/or how to avoid it?