My mousepad inflated?

I kept my computer on a shelf (there were books on the computer if i remember correctly) for a while and when I checked it, I realized that the mousepad was inflated. Mousepad surprisingly still works. Should I be concerned? Are there any risks of exploding, burning etc.?

Note: -Model is Casper Nirvana c350 -I doubt it is battery, you can see (in the last picture) they are far apart, though I'm not sure because the battery has been dead for a long time and can not work unplugged.