So I'm kinda new to singing and taking it seriously. I've been taking lessons and such to get better. Today I was singing a song and at the end I felt a bit lightheaded for like 30 seconds or so. After waiting a minute and taking a drink I sang for about an hour longer and was fine. I was wondering if anyone had an idea of what this resulted from or if you've experienced a similar thing.
You need to build vocal endurance like you build any other kind of endurance -slowly. Singing is a bit easier cause youve been talking all your life so your vocal chords are very used to it - your lungs however, arent (if youre singing correctly). If you sing too intensely for your endurance level your lungs wont get enough oxygen because of the irregular breathing and this will make your not have enough oxygen go to your head - making you lightheaded. Keep practicing like you are and it should go away. don't try to push things - if you feel lightheaded then stop! lol. But if it keeps happening talk to your teacher - youre probably breathing wrong if so.
I kinda thought it was a breathing thing, but my teacher said that my biggest problem is air support while singing and getting enough air out, so that's why it didn't make a whole lot of sense to me that this would happen. But your explanation does help so thanks, you too mr. triumphant as it gave me a little laugh
when you prevent oxygen to your brain you will get light headed... suck air into your lungs using your diaphragm. then exhale 3 times separately keeping your diaphragm contracted as long as possible. good exercise.

You most likly wasnt breathing right whether it was incorrect technique or to much singing between breaths. Try holding your breath till you pass out a few times a day to get used to it.

Just kidding
It happens sometimes. There are a few tracks in my band's setlist which always leave me feeling knackered. You'll improve stamina in time, although you will have a natural limit. Just keep practicing until you get there. These comments about working on breathing technique are of the utmost importance in regards to improving the situation though.