If you've had several semi sleepless nights ( that's when you only sleep four hours or less and probably worrying if that pair of men's running shorts you'll give to your husband will fit or not), then you need at least 10 hours of sleep. I've always thought that just one night of restful sleep (8 hours) will be enough to make our body and mind recover but it is not enough. Researcher have found that sleeping in after a few days of missed sleep can help you recover. It will reduce any lingering sense of fatigue and mental fuzziness.