Oh boy... now you've done it. You've given me free license to megacomment all over this thing.

Much like in your fanfic, Retaining Sanity, survivors could survive on their own, but it would have an extremely detrimental effect on their mental condition. Even to the point of schizophrenia due to loneliness. Humans are social creatures, so we crave SOME sort of social interaction on even the lowest level.

In fact, a thought that just occurred to me is that cases of schizophrenia would pop up all over the place. Through personal experience, I can tell you that your mind can create separate personalities in order to preserve your original mental state. I'm not sure if this is a clinical truth, but this is an observation I have made. It preserves your original sanity by convincing you that you aren't the one doing these terrible things or seeing these horrifying events. I have a friend who I believe suffers from this after a series of traumatic events in his childhood (I also should say at this point, that this is entirely based off of observation. I haven't done any research into this or anything; and as a high school student, I'm not sure how much this input can be taken to heart.)
I have not had anything happen to me to create this symptom, though I can tell you that there have been times when I felt I was not entirely in control of my own actions. Often times, unfortunately and admittedly, this involved violence on a large scale. This could be another response to a zombie apocalypse, due to the sheer amount of violence and gore inherent with zombies.

Even those with the strongest of minds might be affected by the apocalypse. A general feeling of mistrust among other humans would become inherent to everybody, leading people to preemptively kill others out of simple suspicion. This is part of the reason why I, personally, would go somewhere in the middle of nowhere where there is low population density. Like the woods in Mississippi. There is plenty of wildlife to keep a small group alive and small population density would mean extremely low chance of running into zombies.

Strange as it sounds, I think I would go totally medieval mode in a zombie apocalypse. I'm gonna use a machete(since it requires little sharpening) and a riot shield (which I already own cuz I bought it from a police surplus store shutupI'mnormal).

However, there is another way in which I believe my mind would be capable of breaking; and that way is shown in my L4D fanfic (which I will not finish due to lack of motivation). The character, Errol, starts off perfectly sane, however after he is left behind during an attempted rescue, he loses it. He takes on the philosophy that he is already a dead man, so he might as well have as much fun as possible while he can. This involves running from insanely large crowds of infected and special infected, and going on infected killing sprees. I think this is the other way I could go if I do not keep my sanity in an apocalypse.

In fact, multiple times I have thought of having a huge rave in the middle of the zombie apocalypse, killing zombies with strobe lights and lasers and such while a hard bass beats. Obviously, this is an extremely suicidal way of dealing with a zombie apocalypse, but I think it would be fun until the whole death and maybe even un-death... thing... yeah, better keep a pistol with a bullet in the chamber.

I can't say this is how most people would react, since as far as I can tell, I am VERY different from most of society these days. In fact, I would even go so far as I hate society and the people who make up society... but hey, that's part of what makes me me. I can put on a great front for most people who think they "know me."