Some background first...
"Sleep" is not the same as "hibernate". While a machine is sleeping, some hardware components are still active and powered up. In particular, the RAM is getting fed with energy so that its (volatile) contents are not lost. That's why your laptop grew red hot during its time "sleeping" in the warm air-tight laptop bag. You were lucky that time. Since everything worked well afterwards, I doubt the machine sustained any permanent damage.
Hibernation is the act of dumping the RAM contents into a designated file on the hard disk and then literally shutting down, completely. On bootup, Windows reads the contents of the file back into RAM and then resumes where it left off. While it's hibernating, a machine is completely OFF.
There's a third option confusingly called a "hybrid sleep" which causes "sleep" first, followed by "hibernation" if there's no attempt to wake the machine up within a given interval.
How your laptop behaves when you shut the lid - whether it sleeps, hibernates, or shuts down - is configurable through the "power" control panel applet (from memory, I'm not on a laptop right now).
None of that has much to do with your BSOD though. To troubleshoot that:
1) Make sure the BIOS and hardware drivers
(NIC, chipset, video...) are all up to date.
2) If the same 0x9F crashes persist, zip up the contents of \Windows\minidump and upload them here. (You'll need to first copy them to another location on your machine before you can zip them up.)