Utterly Mad

Yeah, I decided that minigame and its jiggy can go eat a bag of bear dicks.

Also, yeah. Check your player options/setup, both it and ZDoom have autoaim intensity in there, including the option to disable it. I tend to enable if playing on the desktop, but leave it on if on the laptop and not using my mouse.

EDIT: Also, Heretic introduced looking up and down to the Doom engine, you sure that it didn't have mouselook in vanilla Heretic?