While reading or watching a movie, i tend to fall asleep really fast. even when listening to a lecture or a presentation. what is wrong with me?

Well...: You could be chronically tired, or not taking enough thyroid medication. Consider the possibility of sleep apnea, or other sleep disorders. Do not panic, and yet see your Dr. This is not normal

Sleep apnea?: A common thing overlooked by many is sleep apnea. You should ask your doctor about it. Sleep apnea is waking yourself up durning the night because of lack of oxygen many times (usually manifests as snoring or gasping during sleep). Your waking up during sleep without realizing it. Your not able to get into the deep sleep stages and are thus tired during the day. A sleep study can diagnose it.

You're sleepy: The most common answer in your age group is inadequate sleep duration at night, so see naps/sleepiness in the day. Increase sleep by 1-2 hours for a few days & check for improvement. If no improvement, then should see your Dr for exam & labs to be sure all OK.