If this is a serious request, drinking water is good. My wife would get light headed, and very weak. Turns out she was low on iron.
I would suggest going to the grocery store and getting an inexpensive multivitamin or iron supplement. It will cost less then $10. If it works you will note it pretty quickly. If it doesn't it won't harm you in the least. I would also take note of your diet. If you are diabetic you likely had a change of diet that day. If your family has a history; if you are overweight, etc.
There are some safe, common sense ways to address. Again, not a doctor just healthy living.
Boo