Crank threads stripped - both pedals fell off
The threads are completely stuffed. Do not just screw the pedals back in and do not rely on loctite or similar compounds. Pedals falling off is at best inconvenient, at worst can lead to crash and serious injury. 

Easiest option is to replace the cranks. Its not a big job but parts cost might mean a repair is a better option for you. The bottom bracket will probably be a square taper, so you need a special tool, or the LBS can do it in a few minutes. 

The only other realistic option is to insert a thread insert (Helicoil) thread repair into the cranks. The left hand crank is a left hand thread. (Park tool have instructions)