Hypotension, I think.

[Pravda]

This isn't a direct cycling thing but I think it's as a result of increasing the kms I've been riding. I've increased my riding to about 250-350km a week and have been noticing I feel faint/dizzy when standing up, usually but not exclusively on days when I've been riding.
What's the solution? I'm looking at booking in a GP visit anyway but in the meantime should I just be eating more?
Cheers.

[jpgibson]

Postural hypotension, sounds like dehydration to me.

[SpinninWheels]

What jpgibson said. I have had the same experience and after asking a doctor while undergoing a full physical and heart stress test he told me it's a result of dehydration, which leads to a lover volume of blood in the system, hence temp drop in pressure when standing up etc. Nothing to worry about - drink lots of fluid while and after exercising.

[CXCommuter]

I had the same problem last year when I was increasing my activity levels (from near zero to ~250km/w). Doc said it was a mixture of the increase in exercise leading to spikes/troughs of blood pressure and dehydration. Basically drink lots and don't do too much too soon was what I was told. Haven't had a spell this year