Moments of lightheadness

[wigglett]

I keep getting very brief moments of light-headedness - what could be causing this?
It feels almost like a pulse or wave of exhaustion throughout my body that makes me feel off balance/dizzy - like I could topple over. It's very very shorted lived - just a second or two - and then I feel fine. It's happening maybe 4-5 times a day.
It happens whether sitting or standing, and seems to happen whether I'm still or moving about.
I've been suffering with a lot of fatigue for the last few months but nothing obvious has come back on my recent bloods.
Anyone got any ideas?

Low blood pressure or low blood sugar maybe?

My bloody pressure is usually around normal - but I wonder if it could be my blood sugar.
My blood sugar (hb1ac) was at the higher end of normal at 38 - I wonder if that could be making me feel funny

Are you drinking enough? Dehydration will make you lightheaded