What would cause these symptoms?

Initial impression is possible diabetic/ low blood sugar issue. That is the most common. Body is very complex. Dehydration, cardiac problem, neurological problem, migraines... Wish I could help more. Go to an urgent care upon onset of symptoms or see if you can check your sugar by using friend or family members glucometer that is diabetic.

Your symptoms sound similar to mine, and I'm anemic. You might want to get a blood test to check for anemia. Also, what are you doing when this hits? Are you outside, maybe? It's been extremely hot this summer. I was out in the sun for less than an hour, and I suffered from dehydration. I was nauseous, dizzy, and weak for three days straight. The only thing I can recommend for this is to drink plenty of water, or an energy drink, as your body may be low on salts.

If anemia, dehydration, or just a plain poor diet isn't the cause for your symptoms, then I'd suggest consulting a doctor. You wouldn't want this developing into something more serious! D:

Part of what you describe sounds like hypoglycemia (low blood sugar).

Do you ever feel this way after eating? If not, and if you generally have this feeling after NOT having eaten for several hours or more, then it could be that you're either running a little hypoglycemic and/or you just need to eat more regularly.

BTW, low blood sugar doesn't mean you need to eat more sugar - that can actually exacerbate hypoglycemia, and in fact, if you're a heavy sugar consumer, that can be making the problem worse.

im not a doctor but should really get your blood levels checked and sugar levels.

it can be anything you can be anemic that makes you very week and you tend to sleep allot and light headed.

but go get your self checked out by a doctor to be on the safe side.

Poor circulation to the brain?

Are you getting up too fast?

How old are you?

Do you have a history of heart disease?

Are you getting enough sleep?

Do you consume caffeine?

Do you smoke?

It could be anxiety. I had that problem and my doctor put me on medicine for it.

go see a doctor .