It is common for babies around the age of 4 months to experience disruptions in their sleep patterns, such as waking up in the middle of the night. One possible reason for this could be teething discomfort. To help alleviate this, you can try giving your baby teething toys that can be chilled in the refrigerator. It is important to be patient during this time as it may take a few days or weeks for your baby's sleep to return to normal. Teething can be a challenging period for some children, but it is a natural part of their development.