Our internal body clock governs our daily or circadian rhythm - telling us when to wake up and when to feel sleepy. Circadian comes from the Latin circa, meaning about and dies, meaning day.
The BBC website has a simple test you can take. This test will produce a chart showing your natural sleeping and waking pattern over a 24 hour period.
If you're having problems sleeping it could be your natural body clock is at odds with your routine.
Many factors can either help or hinder sleep. Here we outline several and provide links to external resources from Wikipedia and The BBC.