The way you describe the process, it sounds unnervingly like the battery could have died during the process of saving, which could have corrupted the file.
Photoshop autosaves files by default, though it tends to delete those autosaves the next time you open Photoshop. But you could try digging around to see if there's a recent one of your drawing still hanging around somewhere. I'm not sure if your Cintiq is PC or Android, but on PC you would want to look for any .psd or .psb files in these folders:
C:\Users\[YourUserName]\AppData\Roaming\Adobe\Adobe Photoshop CC 2018
Auotsave is big plus: I think snapshot clone option would be a great addition to JustSaveIt(mac version) to cover that type of issues. We work on it @wmixstudios