I felt so sorry for Jerry
The biggest theme of this movie seemed to be loneliness and how our character copes with it.
We are quickly shown his well meaning side but we see his incredibly awkward interactions and from that we know he has no friends and no family. Somewhere in his mind, he is also aware of his awkwardness and is justifiably paranoid that others make him out as a joke.
His mind copes with this horrible lonely existence by making friends for him in the form of his pets. Early in the film, he takes his medicine and we see his real lonely existence without any filters.
Specifically, there is a shot of him sitting alone in his chair for what was probably hours. That scene struck me because all of us have felt that sense of loneliness before, whether it is moving to a new place and not knowing anyone, losing a parent/child/sibling, going through a painful break up/divorce. How many of us would've been so eager to take the medication and go back to that lonely existence?
That pain is as intense as a throbbing tooth. People go to great lengths to avoid it. They avoid moving to new places at the expense of their dreams or their careers, they stay in abusive relations to avoid it. Sometimes, it shows up unavoidably, and the one thing everyone asks is "When will this end?"
Sadly, in Jerrys case, the answer is never. In addition to that long dark tunnel, he has mental issues he inherited from his mother and had his mother give him the responsibility of ending her suffering. We also learn that despite his yearning for affection or friendships, he has had none. He had his only friend, the muppet rabbit taken away, he comments that he used to stare into the sky and wish that the stars would become his friends.
We see Lisa bring out his human side although he was already gone by that point. It's also sad bc we know in reality, jerry was likely never going to be capable of having a normal healthy relationship with a person, friendship or romantic because of his mental problems. He was pretty much doomed to a life of loneliness when all he wanted was a friend and a hug.