It sounds like the SSD is most likely failing. The most common way SSDs fail is by disappearing from the bus.....usually when powering on or waking from sleep.
I hope you have a good backup. If not, then make a backup ASAP because you may not get that SSD back online again.
FYI, it is usually a good idea to always provide the exact model of your device when asking for assistance online. You can get this information by clicking the Apple menu and selecting "About This Mac". If you cannot boot the Mac, then you can get this information by entering the system serial number on the Apple check coverage page here, but please do not post the serial number on the forum since it is considered personal information:
View Coverage - AppleCare & Warranty