This happened to me several times with more than one Dell laptop. The solution I have found is to set the laptop to HIBERNATE when the lid closes, not sleep. I

This happened to me several times with more than one Dell laptop. The solution I have found is to set the laptop to HIBERNATE when the lid closes, not sleep. I wish I had known this sooner. This has to be a pretty common issue, I am sure a lot of people close their laptop lid, or set their laptop to sleep and then find their laptop to be an overheated mess in their backpack some time later. TLDR; Hibernate your laptop or turn it off if you plan on putting in a backpack.