Chances are you probably weren't. Actual dreaming comes when ur in REM sleep and that's towards the end of your first dreaming cycle. You probably were having what is called Hypnagogic Imagery (HI). These are little dreamlets, usually short images, that sometimes come with sounds. You experience these as you start to fall asleep. Later on they stop and your sleep gets a lot more relaxed and thoughtlike. At the end of the cycle (which lasts aproximately 90 minutes) your mind becomes very active and you enter REM, where you really start dreaming.

When you have had many dreamcycles, the first part gets a lot shorter and the REM-Phase gets longer. So when u've slept like 8 hours, you can enter a dream within a few minutes.

If ur interested on reading more about the physiology of sleep, just PM me and I can send you material.