What is happening?

 In the last month I have been getting lightheaded and starting to sweat after I am up for maybe a half an hour. My morning routine is to get out of bed & get ready for my day. I shower in the evening so that is not an issue. I thought maybe dehydration since it seems to go away after I start drinking water. Oddly, it doesn't seem to matter if I drink a glass (20 oz) of water before bed or drink nothing. This morning I almost passed out. It doesn't happen any other times of the day. Any thoughts or helpful hints would be appreciated. Thank you!

In my opinion it sounds like either a drop in your orthostatic blood pressure or a hypoglycemic action.  Vitamin deficiences can cause problems like that...B12 or Iron for example.  Have you had your labs checked lately?

 Labs were done and everything seems to be ok. B was extremely high.

Are they testing for everything? How is your vit K level?

If your labs looked good, then it could be a sign of dehydration or another medical problem.  Try to get more fluids in and if it continues see your doctor.  

When are you eating? Maybe change up your routine. It sounds like low blood sugar. I would get up, drink some water, eat, and then get ready and see if that helps. If not, I would go see your doctor.

 Thank you all for some great ideas! 

Rapidly losing weight caused me to have low blood pressure for a while. Like 104/58. It quickly leveled off at normal after my body adjusted, but for a while it was causing symptoms similar to yours. Can you check your BP during one of these spells?

You're about four months out---how much are you eating, and how late in the day do you eat? When I was where you are now, I would wake up nauseous and a little light-headed EVERY morning---until I started eating a protein snack just before going to bed. I also started keeping a glass of water on my nightstand, and every time I'd wake up to go pee, I'd drink some water. My mornings improved greatly once I started doing this.