What is the best plan for creating safe exercise goals

To ensure that your goals for exercising are achievable and safe, first go see a doctor to make sure that handle physical exercise.  Next step is to define what you want to achieve by exercising and by doing so, you would know type of exercises you need.  If you are a beginner, train under a certified instructor to ensure you are doing it right. Exercise at a level that you can do.  Do not over train for it will do your body more harm than good.  Make sure you eat properly and get enough sleep so that your body can recuperate from such strenuous activity.  

Because without physical activity, the body has extra "energy" if you will, and so when it is time for bed you are not tired, so you end up staying up all night. also there is probably an effect on your internal clock, which messes with your melatonin production which goes hand in hand with your sleep cycle