Is feeling a strange movement in the body after Fajr prayer and going back to sleep, or when stressed, considered a wet dream despite not seeing signs of intercourse or direct contact?

If you have a wet dream but do not see traces of semen, then neither ghusl nor sin is required of you, and your fast is not invalidated, because it occurred without intention. As for masturbation, it is forbidden and necessitates ghusl upon the emission of semen, and it invalidates the fast if it occurs during the day and semen is emitted.