Other than depression, what are reasons someone will awaken early (i.e. 3am) with no symptoms (no anxiety, pain, nightmares, cir rythym issues)?

Alcohol: There are probably many reasons, but one common reason is alcohol consumption. Even a small amount of alcohol in the day can have a disruptive effect on the sleep cycle. Some medications can also disrupt the sleep cycle. Ssri antidepressants disrupt the sleep cycle even though they help with depression, which also disrupts sleep. People who sleep lightly need to be careful about these influences.