There are a ton of often-used and always-implausible tropes in this description that you will need to address if you want your story to be even remotely realistic.
Implausible trope 1: Aliens that parasitize humans
Earth biology has evolved alongside other Earth biology for billions of years and every organism has evolved to exploit the same complex chemicals as every other organism. The chances of finding an alien that we can eat or that can eat us (and get usable energy from) is phenomenally tiny.
But even this is nothing compared to the degree of co-evolution that parasites have with their host. Parasites are specifically adapted to exploit specific vulnerabilities in their specific host, and the more specific their mechanism of infection is, the more tightly connected their history has to be.
Finding an alien capable of parasitizing humans is kind of like finding a device created by an alien that had never seen or heard of Earth, and finding that it can not only plug into a USB port but can also run programs on a Windows computer.
Implausible trope 2: Mutations do not work that way
As specific as parasites are, viruses - the only parasites capable of producing specific mutations in a host - are even more specific. Moreover, mutations in existing organisms are limited to alterations in the function of individual cells, not gross transformations of the entire body.
The only parasites that can trigger transformations of the body do so by either physically adding their own body to that of the host (like the louse that replaces fish tongues or the worm that replaces snail eyestalks) or by triggering an existing "transformation" mechanism in the organism. Neither of these are mutations.
To expand on the previous analogy, this would be as if this alien USB could run programs on a Windows computer that made other Windows programs run more efficiently. When the alien had never before encountered any Earth computer before. And significantly more complex.
While it is not impossible to engineer a parasite that causes the transformations you speak of in humans (aside from the telepathy), you would need the parasite to be designed from the bottom-up to cause these specific effects in humans. You would never find this in a natural parasite that had never encountered humans before, and certainly not one that evolved on another planet.
So how to make it plausible?
There is only one logical way that this could happen, and that is if the fungus was engineered by an intelligent life form specifically to infect and alter humans, which it had presumably been experimenting on and observing for quite a while. Why this entity would want to do this is up to you.
As for the specific mechanisms, it should not operate through mutations, but by physically altering the body or triggering existing biological mechanisms. It can damage pain receptors or secrete endorphins to reduce pain, break down myostatin (the chemical that prevents muscles from growing too fast), and increase visual pigment concentration (creating greater sensitivity to light). Possibly the "telepathy" can be explained by the fungus secreting chemicals into the environment relating to its current state, then creating a "tingle" in its host when it detects those chemicals. (This would be less telepathy and more pheromone communication.) It can manipulate the host's behavior by secreting dopamine whenever the host helps to spread the fungus.
It simply lets its hosts be - they have full control of themselves, mentally and physically...and...these fungal-humans to mutate rapidly, gaining an aversion to light and flames, preferring the damp and darkness, slowly losing their eyesight etc.appear contradictory $\endgroup$