Well, you either have paronia or you have a phobia—like phobia of staying alone. In this case a person has irrational fear when he/she is alone in a room. In both the cases you need to consult a psychiatrist and get counseling and maybe some medication. Behavior therapies will help overcome the fears.
The other possibility is that you have insomnia. Physical and emotional stress, depression and too much intake of caffeine during the day could also be a cause. Hence cut down on coffee if you take this, try and go for brisk walks in the evening, avoid sleeping during the day, and take a warm glass of milk at bed time. Try yoga, it helps. See if these tips help you. Other causes of insomnia include , allergies, asthma, high blood pressure, heart disease, arthritis, hyperthyroidism, and sleep apnea. You should ideally consult an internal medicine specialist and a sleep specialist for this. If no cause is found then some counseling may help.
Please consult your PCP for primary examination followed by proper referral.