Insomnia: Why can't I stay asleep? - Mayo Clinic

Waking up in the middle of the night is called sleep maintenance insomnia, and it's a common problem. These midsleep awakenings often occur during periods of stress, but depression could be a factor. Sleep maintenance insomnia may also be due to sleep apnea or restless legs syndrome.

To help stay asleep through the night, try some stress-reduction strategies....