I don't remember your username so I'm just putting this out there.
Last week I tightened my disk brakes, specifically at the cables. They had gotten to the point I had to pull the levers all the way to the handlebars and were still feeling weak.
After a little adjusting (I made the front one a little too tight at first) they started feeling great, but this morning on the way to work they started feeling really weak again, like they were barely engaging. Only this time, the levers don't go all the way to the handlebars, the travel distance is the same as when they were doing fine, so it's not that the cable has slipped.
I don't want to over-speculate since I haven't really done this sort of thing before, but I'd appreciate advice on things to check. My workplace has a ton of tools I can borrow if need be.
Okay, final (I hope) update: there was a very well hidden knob that adjusted the position of the brake pad, which is what I actually needed to adjust the whole time. Thank you all for your advice and suggestions, I learned a lot about bike maintenance and I apologize for being a stressed out mess. Yall are cool.