When i was trying to sleep i had some internal shaking near my abdomen and legs. i'm not really stressed so what could it be?

Exercise?: There are not many details to go by in this question. If you were doing a lot of abdominal and leg exercise earlier in the day the muscle might shake from fatigue. Restless legs can give a sensation of movement. Shaking is a not a familiar symptom of internal disease, or urinary infections, unless the whole body shook, and you had a fever.

Myoclonus?: Some folks' bodies jerk as they are falling asleep, they may experience this as pleasant or unpleasant (myoclonus). The entity to rule out is restless legs which can be a life-ruiner. Please read up on both, and thanks for asking.