The reasons vary with each person but the things that help one sleep better can be used by everyone. Worry, depression, pain, and medications are the chief reasons most people have trouble sleeping. Lets discuss medications, first. Many medications contain caffeine or decongestants that can keep people from sleeping well, if they are taken too close to bedtime. The only way to know for sure is to look at the label.
Caffeine is easy because it is usually listed that way.
Decongestants have various names but the box or label usually has the word decongestant somewhere. All decongestants can be stimulating and cause one to feel nervous. Decongestants are found in many cold and cough medications as well as allergy treatments. Many prescription antidepressants such as Prozac, Paxil, Zoloft, and others can be stimulating to the effect that they interfere with sleep. Those of you who take herbal medications such as St. John's Wort or Ginseng must be alerted to the fact that these herbs can also be stimulating enough to interfere with sleep.