What are some causes for difficulty falling asleep?

Insomnia: Many causes of insomnia, including substances like caffeine and amphetamines plus many medications. Depression and anxiety can both cause difficulty falling asleep. Post-traumatic stress disorder can interfere with sleep, and can also cause nightmares that wake you up and then not be able to get back to sleep. Discomfort in the room, like too much noise, light, or temperature also.

Insomnia: Possible causes of insomnia include: poor sleep hygiene,Traveling with change in time zones, chronic pain, frequent night-time urination, problems breathing, Shift work, anxiety disorders (esp. PTSD), Depression, stress, bipolar disorder, medications (i.e. stimulants), caffeine, alcohol, eating large amts before bed, aging, restless leg syndrome, sleep apnea, etc.