I also had the Admin bar disappear without any warning. Here's what I did since I'm not a coder ... not even a LITTLE bit. In my case I determined that the culprit was my theme that was causing the problem. The name of the theme is not important; I've had this happen before with other themes.
1. Backup your freakin' site! And I mean EVERYTHING! I highly recommend the UpDraft Backup and Restore plugin.
2. Change the theme of your site. It doesn't matter which theme you use. We're going to change it back to your original theme in a minute.
2. Since Bluehost hosts my WordPress site I use a File Manager to find any folders that look like they would likely contain files associated with the theme I'm using. If you're hosting the site on your own server then you would know how to delete files and folders on your machine.
Be SURE to delete the FOLDER itself (the one containing your bummed-up theme) once all the files contained in them have been deleted.
CAUTION: Don't get careless or SLOPPY and delete folders that obviously don't have anything to do with your theme. You'd be ASKING for trouble. Don't say I didn't WARN you!
3. Once your old theme files and folders have been 86'd then go back to your site, search for the original them, and RE-ACTIVATE it.
Once you've done all this everything should be A-OK and your Admin bar will have magically been RESTORED to the top of your screen!
If I can do this, YOU can do it! Just don't get in a big hurry!