Nearly half of the adults polled in a 2011 National Sleep Foundation survey admitted to rarely, if ever, getting a good night’s rest. That could explain why handfuls of people you run into at the gym are so cranky, as well as why those sleep-deprived zombies might have trouble powering through and recovering from hellish training sessions.

“You give your body the chance to repair, recharge, and regrow during sleep,” says wellness expert Dr. Felecia Stoler, DCN, MS, RD, RACSM. “It’s the ideal time to replenish nutrients, and, since your body isn’t moving, it allows the muscles to repair themselves.”

Along with inhibiting the production of growth hormone (GH), which increases during deep stages of sleep, sleep deficiency can curb energy levels, diminish alertness, weaken the immune system, and cause you to be more … uh … forgetful.

So how much sack time should you be getting? There’s no hard-and-fast rule; aim for seven to eight hours per night. And despite certain sleep issues like sleep apnea requiring a polysomnogram to detect—polysomnogram is the fancy word for sleep study—others can be corrected with simple tweaks like these …