If you hold your breath while you’re doing crunches, you’ll start to feel lightheaded and dizzy. You may also feel like you have to throw up. This is because your abs are not meant to be overworked, and will get tired very easily if you hold your breath during your exercises. Make sure that you’re breathing properly during your crunches in order to make sure that you’re working your muscles in the right way while preventing yourself from hurting yourself.