Headcanoning Sam as a schizophrenic person.
Context: diagnosed, (re)watching with my person, we are on season one.
So I have to admit that when I originally watched the series the following didn't strike me the way this now strikes my partner especially in the episode of and after 'home'.
To stress, everyone's mental health is different and even the people with the same diagnosis can and will have wildly different experiences. Still I do admit to seeing part of what she's seeing and what she says to be seeing is behaviours that are very similar to mine in times where I have a tougher time managing my symptoms and even just in the day-to-day.
Season 1 Sam is an introverted rambler, great academically and sure of himself (so sure of himself that he drives a car into a building on a hunch that it could work), he's the type of guy that constantly makes assumptions and reaches for conclusions even though these often prove to be right. Especially in the beginning Sam holds on to the idea that they have to find their dad to kill the demon like his life depends on it, tunnel vision bordering on obsession not unlike John, still he's empathetic and trusts his brother like no other. Dean does mention Sam seemingly having had some personality shift, he's acting like him, shoot first ask questions later. Ultimately he can't stop thinking about the dream he had of Jessica dying and it consumes him quietly.
On its own these are just quirks, consequences of seeing his girlfriend die like that, of being back on the road with his brother just like that, however someone that either has been around people with schizophrenia, delusions or experiencing psychosis or that has read the dsm 5 for whatever reasons might see certain similarities between the behaviours and the symptoms of the disorder which unlike often portrayed isn't just about hallucinations but for a very large part also about the way of thinking, the inability to tell the mind no, the way it twists and turns into something disorganized that only makes sense to the individual, the way especially when left to its own devices it will keep on going and going until the individual cannot step outside of their own thoughts.
Then we see Sam's visions happen for the first time.
It is something that consumes him, that he doesn't question despite aknowledging he knows it sounds weird but 'you just have to trust me alright?' he sees signs and links them to other signs, grabbing onto one small detail and just going with that (here the tree, drawing it over and over). All things considered, if he hadn't been right here this could have counted as a delusion or as the behaviour fitting to experiencing those.
I'm personally not sure how I feel about this observation but I relate to it and it puts some of Sam's behaviours I've been annoyed by in the past into perspective, gives them some reason, even the way he becomes less snarky and energetic and just less 'season 1 Sam', in the pov of schizophrenia this can be described as what is called the negative symptoms which can out itself in lack of motivation, becoming withdrawn, and even (for those that like to complain about those) a reduced range of visible emotions among other things.
It's funnily recognizable in the way he isn't the one driving the impala too or how he gets uncomfortable in social interactions, one would almost wonder if Dean knows judging by his behaviour.
The next episode being called asylum and featuring Sam in a therapist's office doesn't help not headcanoning schizophrenic Sam Winchester either.