Why do i get a minor panic attack as i am falling asleep (ust drifting into sleep) ?

Anxiety and fear: There are many individuals in the populations that experience increased anxiety related to the start of sleep. There can also be hypnagogic and hypnopompic psychotic experiences that are a function of the initial intrusion of rem sleep at the start of sleep or the intrusion of wakefulness into rem sleep that produce transitions in sensory and neuromuscular function that can be distressing to many.

PA or hypnic jerk: The timing of your so-called panic attack is highly unusual. Although most nighttime panic attacks occur in the first half of the night, they are rare just as you're falling asleep. What is much more common at that time is a hypnic jerk which is also referred to as a sleep start. Please see: thescienceofsleep.Wikispaces.Com/the+hypnic+jerk.