My baby girl is about 4 months old and she constantly arches her back. This is a really new behavior and it makes me nervous. She did it in her sleep last night, and after reading about sleep apnea in babies, I'm scared she's going to stop breathing. I've set her down a few times and she's done it too. I'm just worried after reading some of the many reasons for arching backs, such as apnea, gerd, infantile spasms, epilepsy, cerebral palsy, autism, teething, full, gassy... it's so much! Has anyone experienced this?