Just make sure you eat a bit of food before your workout, and then have a recovery meal after the workout. I know after some intense workouts I feel dizzy and light headed but once I eat some food I feel great again. Personally I eat a bowl of plain oats with milk before I work out, the milk gives a bit of protein, and the oats are complex carbs which give your body plenty of energy for your workout, and then after the work out I eat something rich in protein to build back muscle fibers. I love my eggs, there simple and have a lot of nutrients in it.
Side note for guys working out, always push yourself beyond your limits, if you want to see good gains you need to keep pushing yourself. It's not necessary if your just trying to lose weight but if your trying to get a lot stronger, and put on a lot of muscle, the fastest way to do that is to constantly push yourself and eat a ton of food. I speak from personal experience.
You are either overdoing it, havent eaten enough calories that day, or arent staying hydrated enough. Never push yourself beyond your limits and know when to stop, be sure that you are eating properly and consuming enough calories during the day, and drink plenty of water while your working out.
Probably because you haven't aten. It's bad to workout with an empty stomach and bad to eat with a full one. If i dont eat i usually get headaches and feel lightheaded.Try to eat a gronola bar or something. That should make you feel better(:
you might not have had enough to eat before you worked out, or enough water!
Your working out too much and eating less.