What did you do to this USB flash drive last time? Did you extract it without using “safely remove hardware”? Did you use it without antivirus scanning? Or did you drop or fall it to the ground?
In short, I hope you can learn a lesson to use your USB flash drive safely and rightly all the time.
But, now, in order to rescue your stored data, do not format or overwrite this USB flash drive. Just plunge it to your computer and try to restore them all back by using some data recovery software like 4Card Recovery, Recuva, Power Data Recovery and more.
NO matter which one you use, just scan your USB flash drive more times to get back your files as many as possible.
Make data backups all the time in the future.