I know the feeling, definitely light headed and always wake up with a headache sometimes like a horrendous hangover and no not been drinking either, used to love a glass of wine. I can drink a lunchtime but I think because I am more hydrated in the day. I do try to drink a glass of water before I go to bed which does help the headaches, I notice headache worse if I forget. We obviously get dehydrated in the night. I also drink lemon water throughout the day which really helps with hydration.

Good luck with the haematologist.