I mean, the main character is an experiment. In gunsaw, it is stated that experiments are quite emotionally sensitive. Ngl, I'd feel the same way If i was in the middle of nowhere, underground, just forced to kinda... Dig nonstop and find stuff and deal with injuries myself. The point of the game is to show how hard the odds in such an environment is.
The inability to heal is chance-based, so if you keep trying to heal, unless your character is INCREDIBLY DEPRESSED, in which you'll be more worried about your character literally trying to worsen his conditions by harming himself rather than the inability to heal.
The best tip I can give though is to prevent depression, which wasn't likely entirely caused by your character suffering an injury. Looking at corpses, eating really nasty stuff like your own species' parts, and generally just not tending to your character's wants and needs can cause them to get depressed fast.
Stuff as simple as feeding your character geofruit, or really anything that seems tasty for that matter, and playing carefully as to not physically push your character too hard will easily help prevent depression.
Stopping depression is kinda different though. You CAN try to use geofruit or tasty things, but at that point you might need some assistance, not just from drugs, but also probably stuff as simple as looking for comfortable places to sleep and hypothetically, possibly some social interaction with survivors.
The depression system is really complex, if you have any questions, I can help you figure them out.