i exercise for 60-70 minutes continuously at the gym and end up loosing 400-500 pounds and then i take a small 10 walk.is it ok to sleep off after coming back from d exercise immediately

No, its not OK, most of human growth and rest takes place during sleeping.
You need to avoid strenuous activity in the last ~3-4 hours before sleep, this is because your blood pressure needs to be low in order to sleep, and keep in mind that during sleep, your blood pressure really gets low (alternating).
The best thing is to go to the gym and whatever you said in your question and finish ~5 hrs before sleeping, then shower, clean up and rest in front of television or something then go to sleep.
The catch is not to eat much before sleeping, maybe a glass of milk, some fruits and thats all, no more (it'll get processed as fat) and no less (empty stomach will be a nuisance and would lower your metabolic rate, which is your body's body weight-saving mechanism, it minimizes the loss of fat).

yes, after you cool down. good luck!!!!!!!!!!!!

Lets put it straight. Losing weight is not that hard, You will never hear me say that it is. All it takes is dedication, motivation and hard work<!--There are some fairly simple changes that will greatly improve your chances of weight loss success. Check this out to loss weight,
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The best, most effective way to lose weight and keep it off is to simply eat right and exercise. Good diet, minimize saturated fat, use monounsaturated fat-->Always check in gradients of everything you are buyingRelaxation, stress and strain never allow people to be slim.

It won't hurt your weight loss.

During the average sleep a person burns approx. 200 calories. The figures you put on this question are not written correctly. You are not loosing 4-5 hundred pounds at a time. You need to re word this so you can get a more accurate answer.

No harm in sleeping after exercise.The sleep will not interfere with your wt.loss program.

If you have lost 400 500 lbs. you don't need to be asking you need to be telling.

If you lost 400-500 lbs, you probably do need a nap. Go for it!