Bad day? Not so much through my comic. I've had times that I went and drew an intense sketch or illustration to deal with intense feelings, but there's such a long, uh, production gap in my comic that it's not a great source of immediate catharsis -- if I were to insert something new into my comic, it would be years down the line before I officially drew it happening. By then, I would probably be over my bad day. xD
But I do think some things about the stories I tell are ways of processing bad experiences, or coming to an understanding about parts of my life that were hard. I think it's something that happens in the background -- it's not like I sit there going "well, now I'm going to invent a way to process the emotions associated with this difficult event and put it into the story!!!" it's more like, I'm designing a villain with an unnaturally prolonged life for a story, and suddenly notice that this character is tapping into a lot of my own horror from experiences with family members who suffered through a prolonged death, and then go "ohhhhhh I see where this villain came from" and kinda lean into it, pouring a lot of those emotions into that character, trying to pull from the things that were personally intense for me. Not so much venting bad emotions as just.... trying to let myself speak honestly about the experience, even if it's translating it into a fantasy or sci-fi context.
There's absolutely a kind of catharsis that can come out of that, but it's a longer, slower process -- very different from the feeling of sitting down and drawing a sketch with a lot of blood in it because I had a rough day.