Tooth pain at night when I lay down?

See dentist. See dentist. Probable bad tooth. If pain does not occur at night until after your fall asleep, may be due to grinding/clenching of teeth with resultant dental pain.
See your dentist. You may have an abscess or other problem with the nerve of the tooth. Please have it evaluated by a dentist.
May be infected... If the tooth does not hurt at all during the day, or with a stimulus such as heat, cold, or chewing, you may have a sinus problem. It also may be in the beginning stages of nerve death....Kind of hard to say. Keep a close eye on when it hurts, and if at any other time it bothers you, get to the dentist pronto! if it is only at night, take a decongestant before bed and see if that helps.
Root canal. Oftentimes this is the result of an infection in the tooth. Sleep on 2-3 pillows to raise your head until you have a chance to visit a root canal doc ( endodontist) to have it evaluated.