What's that sinking/falling feeling you get?

[ASecretLemonadeDrinker]

I've had it a few times in the past, but the last two days every now and again I keep getting a sudden dropping type feeling come over me - hard to explain, I guess a little like swinging down on a swing with your eyes closed? What is it?
Thanks

Are you worried about something?

For example, do you have a child about to get A-level results on Thursday .

It's exhaustion in my case

No, not actively. Dh is getting exam results soon mind, but I had forgotten about those

I was just about to type I am utterly exhausted, but wasn't sure that was it because I am not sleepy, it's not nodding off sort of thing

I know what you mean. (awake but exhausted)
For me it's a sign that I'll need a topping night's sleep three nights in a row.
(But I am not a dr)

low blood pressure?

Could be low blood pressure, or could be heart arrhythmia?

Ears?

I was about to suggest an ear thing.