I have joined the gym is that a good choice?

I have just aplied to join the gym need to do some exercise is this a wise choice? I no they say not to do alot of exercise but I don't fully understand why. help!

Your body has to get used to the reduced calorie intake, you should wait a few weeks before starting. Once you start you must listen to your body as soon as you feel any pain, dizziness etc you must stop. You are likely to get dizzy spells if you do too much. You woill also need to drink much more too.