Sleep is needed for physical and emotional health and is important to maintain optimal brain function and general tissue health. In the young, sleep is critical for normal growth and development.

The beneficial body processes that occur during sleep are too numerous to list completely, but a few of the more important items reveal how critical a good night’s sleep is to optimal health and wellness.

Read on to find out about five reasons why you can’t fall asleep.

1. You are training too late in the day

Sometimes we just have to fit in exercise whenever we can, but certain times of day can be costly to our rest. Working out too close to bedtime can be overstimulating, causing us to lay wide awake when we should be slipping softly into sleep.

“Exercise close to bedtime can make it harder to sleep, because it can make you overly alert,” confirms Sack. If you can’t fit your workout in earlier, try calming exercises like yoga or tai chi.

2. You are drinking too much caffeine

While it may seem obvious, caffeine is a sneaky stimulant that often interferes with sleep. Consuming too much of it can lead to staying awake in bed for hours.

“Many people may be ingesting a lot more than they realize, because it’s in a lot of things besides coffee,” says Sack. Check the labels of your energy or sports drink or other supplements, such as Hydroxycut, to see if it contains the potentially sleep-wrecking ingredient.

In addition, weight-loss drugs, including inula racemosa, may contain caffeine. Other supplements, including Glycine Propionyl and L-Carnitine, may be associated with sleeplessness. Green tea (and most other kinds of tea) also contain caffeine, so be careful if you’re drinking it or taking it as a supplement. Always read the label first and discuss supplementation with your doctor.

3. Too much light exposure before bed.

It’s easy to zone out in front of the TV or your smartphone after a day of work, but when you’re exposed to blue light in the evening, it can disturb your sleep cycle. This light emitted from electronics can delay your sleep onset, causing you to lay awake in bed.

The bright light from TV, video games, or iPads can trick your body into thinking that it’s morning rather than bedtime.

“Lights signal to our brain that it’s time to wake up, so if you’re watching TV close to bedtime, it may disrupt your sleep,” says Phyllis Zee, M.D., director of the Sleep Disorders Center at Northwestern Memorial Hospital in Chicago.

Move the TV out of the bedroom so you’re not tempted to tune in. “You want to associate your bed with two things: sleep and sex,” says Dr. Sacks. “It’s easier to fall asleep when you link lying down in bed with sleeping, and nothing else,” he explains. Alternatively, take advantage of apps like f.Lux or the iPhone’s “Night Shift” feature, which makes the screen light redder to help you fall asleep faster.

4. Inconsistent sleep schedule

If you don’t go to bed and wake up at the same time every day, you simply cannot get the rest your body and mind need. A consistent sleep schedule will synchronize your body’s internal clock, so you feel sleepy at a regular time every night.

5. Stress.

Stress and worry from events in your personal or professional life might cost you precious sleep at night. Overthinking, being anxious, or just stressing over things you can’t change activate might lead to chronic stress and interrupted sleep.