What could this be?

On two separate occasions (about 2 months apart) I experienced becoming very faint, my legs going numb/tingling, dizziness, and my vision going in an out with black spots(like tunnel vision). The first time this happened I had been standing for about 2 hours working nonstop. The second time I had just gotten out of... show more On two separate occasions (about 2 months apart) I experienced becoming very faint, my legs going numb/tingling, dizziness, and my vision going in an out with black spots(like tunnel vision). The first time this happened I had been standing for about 2 hours working nonstop. The second time I had just gotten out of the shower. Each time this happened I had gone quite a while without eating and Ihad to drink something in order to feel better, and once I did I was perfectly fine. I also sometimes have difficulty standing in place for long periods of time because I eventually get dizzy and feel sick. I also often get dizzy and lightheaded while I'm taking a hot shower. What could be causing this? I'm a 20 year old female, about 5 foot 7 and 120 lbs, so I'm not anywhere near overweight.
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