A child sitting up and laughing at night is not necessarily epilepsy, it may be caused by dreaming, or it may be related to epilepsy and other diseases. 1. Dreaming, if the child is more excited to play during the day, the symptom of sitting up and laughing may occur during dreaming at night, which is usually normal. 2. Epilepsy, if the child has epilepsy, due to abnormal discharges of brain cells, which may lead to neurological disorders, may cause the child to sit up at night, involuntary facial twitching, and seemingly smiling. If this is usually a frequent occurrence in your child, it is recommended that you take your child to the doctor promptly to determine if epilepsy is present. If it is triggered by epilepsy, it can be treated with medication and other treatments under the guidance of a doctor.