A: Eng, this is one of the most common concerns that parents have—how to help your baby (and you) sleep through the night. Since your baby was sleeping through the night for the past few months, this is hopefully only a brief interruption and you can help your baby get back on his sleep schedule.

Why did your 5½-month-old start waking up at night now? Babies have natural sleeping cycles that bring them into lighter levels of sleep periodically through the night. Although the expression, “sleep like a baby” implies that babies sleep soundly throughout the night, in fact, babies commonly awaken during the night and fall back to sleep.

Any change in your baby’s life could temporarily throw off his ability to put himself back to sleep. Teething, advancing his diet to solid foods, weaning from breastfeeding, beginning to crawl, parents returning to work, having a new caregiver, beginning separation anxiety and stranger fear, moving into a new room or crib, going on vacation, or having an ear infection could briefly throw off your baby’s sleep patterns.

Here are some tips to help your baby re-learn to sleep through the night: be sure that he’s eaten enough—by 5½ months old, he can eat solid foods such as cereals and pureed fruits and vegetables several times a day, and 16-24 oz. of milk a day—including a good meal of solid food and milk in the evening.

When he wakes up at night, give him a few minutes to see if he’s just fussing a little and can put himself back to sleep. If he continues to cry, check on him—it can be helpful to have dad do it rather than mom—but don’t turn on the light, pick him up, or feed him. Reassure him in a soft voice or pat him gently, then leave again.

You can continue this pattern of waiting and checking on your baby until he falls asleep. It can be heartbreaking to listen to your baby cry, but if you’ve ensured that he’s okay, try to stick to the plan because your consistency will pay off. Each night, extend the amount of time you wait a little more, until he re-learns to settle himself back to sleep.