Is leaving a Teflon rice cooker on overnight dangerous? I own a cheap Rival brand rice cooker. Here is a link to the product page. Note that there is an inner removable bowl where the rice is cooked. This bowl is coated in Teflon.

After cooking rice last night, I forgot to turn the cooker off, although it automatically switches to a 'warm' setting after the rice is done. (The two settings can be seen in the product page linked above.) I forgot to unplug the cooker, and it remained on overnight (8-9 hours) in a small, poorly ventilated apartment. Should I be worried at all about possible Teflon fumes? The bowl was only mildly warm when I found it in the morning, and there was no evidence of burning. I was under the impression that Teflon is only dangerous at very high temperatures, but I wanted to be sure.

More generally, suppose I want to start making rice at lunchtime so that I have warm rice ready for me when I come home. Is it safe to leave the cooker on for this period of time?
There is no risk to the Teflon itself, or from it; PTFE breaks down at about 500 F, which rice cookers will not achieve, especially on warming setting.  Other than that, PTFE is one of the most inert substances known to man, as the atoms are already bound in energetically very favorable bonds:  little is as able to displace them without significant input energy (thus the high breakdown temperature).

On the other hand, you should not hold rice for a long time without either refrigerating it, or having it above 140 F (60 C) as there is some risk of Bacillus cereus growing and causing food borne illness.