It is natural to feel low and miss the person you have lost. However if it is interfering with your sleep, studies or general well being, or if you feel suicidal, you need to consult a psychiatrist. It is common to feel low, cry, feel like you are alone, or lose your self confidence. Usually time is the best healer. However if things are too difficult to handle you should talk to a psychiatrist or counselor. Confide in someone close to you, who will support you in this difficult time. Don't cut off from friends or family, even if you feel like you want to be alone.
Do not take any medication on your own without the advice of a doctor. Taking sedatives with alcohol can cause aspiration, disorientation, loss of consciousness, brain damage, etc.