Is a dryer vent hose that popped off something I can fix myself?

You can absolutely do this yourself, it's about as easy as appliance fixes get. Slide the dryer out, push the hose back onto the dryer outlet, and secure it with a 4-inch worm gear clamp from any hardware store, a couple bucks. Also check the other end where it connects to the wall vent, since if it slipped off one side it's prolly loose on the other too. Clamp both ends and you're done.

Did this same fix at my old place, the hose had come loose on mine too and it was literally just push it back on and tighten the clamp. Took ten minutes. One thing I remember is the hose had a bunch of lint packed inside it, so I shook it out over a trash bag before hooking it back up. Felt way better about it after that since all that fluff near a hot machine seemed bad. Do you need to unplug the dryer first to pull it out from the wall, or can you leave it running while you work?

When mine did this a couple winters ago I went to reuse the old foil hose and it was so torn up at the collar it wouldn't seal no matter how much I tightened the clamp. Ended up grabbing a short piece of semi-rigid metal duct for like ten bucks and that was the thing that actually fixed it, no more dust pile and the loads dried in one go. If your hose looks crushed or ripped anywhere just swap it, it's cheap enought that it's not worth wondering.

While you've got that machine pulled out, take a peek up into the wall vent pipe. Back when I was doing this stuff with nothing but a flashlight and a coat hanger, I found half a sock's worth of junk wedged in there more than once. A lint brush kit on a pole runs cheap and lasts forever. Also go outside and make sure the flap on the vent hood actually opens when the dryer runs. If it's stuck or the screen's clogged, no clamp in the world fixes your drying times. My mother's dryer took forever for years and it turned out birds had nested in that hood.

Update: got it back on with a clamp and tightened everything down, loads are drying way better already. But I poked a flashlight up into the wall duct like someone suggested and there's definitely some fuzz hanging in there, can't tell how far back it goes. Is that lint brush kit thing actually easy to use, or tricky to get the angle right going into the wall?