There is a condition called as thoracic outlet syndrome, which can be responsible for your symptoms. Due to an inadequate passageway from neck to arm pit, the nerves and arteries are pinched and this can cause sleeping of arms and hands. Please read about the thoracic outlet syndrome in this resource;
Investigations needed to establish the thoracic outlet syndrome are;
a) Chest x-ray
b) Neck x-ray
c) Magnetic resonance imaging (MRI) and computed tomography (CT) scanning
d) Doppler and plethysmography studies
Treatment is as following;
1) deep electrotherapy (therapeutic ultrasound),
2) electric stimulation,
3) superficial heat (Hydrocollator packs),
4) stretching exercises,
5) postural correction exercises,
6) strength and endurance exercises
7) surgical intervention like first rib resection.
Please feel free for your follow up questions.