There are all sorts of analyses of Superman based on the new movie. I'm going to look at the classic Superman - the Silver Age one. This is a little complicated because the character was developed by multiple writers, many of whom had little knowledge of science.
Officially Superman's strength and invulnerability came from his planet of origin, Krypton. It was described as being so massive that its gravity was many timed Earth's. That was fine when Superman was jumping tall buildings but it doesn't explain other facets of Krypton. I don't think anyone ever said it but the gravity on Krypton must have been so immense that it collapsed all matter on the planet into a new form. That includes both animate and inanimate objects. That is why Superman can only be cut by metal from his home world.
The other source for Superman's powers is the Earth's yellow sun. This puts out energy on some unknown wavelength which can pass through the entire Earth at night but are intercepted by Superman's body. These rays give him extra abilities such as flight and X-Ray vision. The mechanism for this is unexplained.
Most later writers simplified this. Superman's powers came from the sun, period. In some cases, simply exposing him to the rays of a red sun stole his powers.
I saw a discussion about why Superman didn't have PTSD. The best insight on this came from the Dark Knight Returns where Batman is speculating on the differences between them. Batman's parents were killed before his eyes when he was old enough to understand what it meant. Superman was so young that he had no real memory of his real parents. He was raised by a loving couple so his childhood was idyllic.
I can make a case that Superman did have a fixation on his native planet. He traveled there often (using a time travel device since he lost his powers as soon as he was there). He met his parents on several occasions.
Sometimes his fascination with Krypton got a little creepy. Consider the bottled city of Kandor. The entire city was stolen from Krypton before its destruction by an android known as Braniac. After recovering the city he kept it as a trophy in his Fortress of Solitude. Supposedly he was searching for a way to restore the city to its original size but there was nothing to stop him from simply opening the bottle and letting a hoard of tiny Supermen set up housekeeping where ever they wanted.
The fact that fragments of Krypton were converted to kryptonite which was lethal to Superman must have been confusing. You can't go home - because it will kill you.
Between losing his powers if he went to Krypton in the past and having pieces of it try to kill him in the present, there was plenty to ward off survivor's guilt.
One of the most touching stories about Krypton involved Superboy discovering that his parents were still alive in suspended animation. With the help of his adopted father and at great risk to both of them, they recovered Jor-el and Lara only to play a recording in which Jor-el revealed that the two of them had received a lethal dose of radiation. He hadn't told Lara and the suspended animation was to keep her from despairing in their last few days alive. If they were reanimated they would die quickly and painfully. So a teenage Superboy had to choose between meeting his parent and assuring them a painful death or leaving htem as they were. As always, he made the correct choice regardless of the cost to himself.