Best way to record sleeping, at least the last several minutes.

I am looking for a relatively low-cost, low-resource way (e.g. in terms of file size) of recording me sleeping, at least the last 10 minutes or so before I wake up, but preferably longer. The goal is to observe particular behavior during my sleep. The video quality doesn't have to be great (CCTV-like quality could do), and it doesn't have to be in color. In fact it would probably need some sort of night vision option if I'm leaving the lights off.

I'm not sure if the best tool is a webcam or a regular cam, and in either case, which to use. It should have the ability to record objects clearly in the dark, and allow the user to set a recording time frame (e.g. 10 minutes) so that older content is deleted as newer content comes in. And considering that it might be recording for hours, it can't take up too much space on whatever storage space is being used.

Thanks for any help.

Edit: Here's what I mean by the 10/etc. min. recording time frame:
The recording continually records until it's manually stopped, but it only keeps the last 10/etc. minutes on storage (primarily to save storage space, but also because I'm checking mostly for behavior that might occur close to or while waking up), and after I wake up, I can stop the recording.