There can be many reasons for not being able to sleep:
- negative stress and depression
- symptoms of stress
- psychical pressure
- too low or too high blood pressure
- cronical pain
- having a cold
- allergy
- thyrotoxicosis
- sleep apnoea
- restless-legs syndrome
- riot
- drugs
- alcohol, caffeine
- too soft/hard mattress
- too much used air inside the room