This is a toughy. Most of us don't have as much control over the amount that we sleep as we should. Work, family, education, housekeeping, and so many other tasks can literally prevent us from getting the amount of sleep that we need.
However, as the experts tell us, getting enough sleep actually improves metabolism. On the other hand, people who are constantly sleep deprived typically find that they have less energy to do regular, daily activities; including digestion.
As a result, sleep-starved people often lower their own metabolism. They simply don't have the strength to break down food efficiently, particularly carbohydrates.
This is a very difficult issue, because many people can only find time to exercise by borrowing from their rest time.
For example, after a long day of work and dealing with family and home commitments, a person may find that the only time they have to exercise (and thus boost their metabolism) is late at night; say around 9:00 pm, or even later. So what should one do?
Ultimately, it's a question of balance. Naturally, if you're willing to exercise, and your doctor agrees that it's healthy for you to do that, then you're not going to get fit by sleeping instead of exercising.
Yet with that being said, if you steal time away from your sleep/rest in order to exercise, over time, you can actually do more harm than good; because the following day, you won't have enough energy to digest what you eat. The answer to this catch-22 lies in balance.
You don't have to work out every night. Or perhaps you can integrate a workout into your life during the day; maybe at lunchtime or right after work.
Most fitness clubs are open very early (some are even open 24 hours), and if you choose to workout at home, you can do so in a generally affordable way (while some machines can cost thousands, basic machines that get the job done only cost a few hundred, even cheaper if they're used).
If you find that you have trouble sleeping, then this can also negatively affect the speed of your metabolism (because you won't have enough energy the following day). Insomnia and other sleep disorders are very common problems, and there exists a variety of support systems in place to help people get the rest that they require. Some non-medical tips to help you fall asleep include: