Stages of sleep REM etc

Hi,

Can someone please tell me what happens to your sleep/rem cycle when you get woke up in the night. let try to explain, i understand the rem cycle and that it gets longer throughout the night. Also some people suggest to set an alarm about 4.5 hours into sleep so your woken out of a dream and because of this dream recall should be better.

What if you wake up 2 hours into your sleep say by a child or noise or something else and after say 10-20 Min's you go back to sleep will your sleep cycle carry on or will it reset. when you eventually get to that 4.5 hour time will your rem still be as long as if your stayed asleep?

Small changes don't seem to alter your sleep cycle much. In your example, your sleep cycle would probably remain unaltered. If it became a habit, or happened every night, you would probably adjust a bit to accommodate.