Regardless of whether it was a repressed memory or his brain doing random shit and being mean to him, that shit shakes him the hell up. Like, jolt out of bed in the middle of the night level, eyes blown wide, labored panting, cold sweats, needing a few moments to realize it was just a dream. Picturing the dream happened loooong long down the road, maybe even by the time he was a mercenary working for the Admin or even Gray Mann (in which he might wake up Cheavy). The "get him pregnant" part sticks out the most to him, and inspires Medic to do the baboon uterus experiments, driven to make cis mpreg a thing. Perhaps feeling the need to either relive the nightmare to make it real in some form of taking control, or wishing to inflict it on someone else (eg. Team Classic). Maybe he'd want his partner to pretend to be his vati and tell him he's going to get him pregnant, now with the newfound risk of that actually happening.