Welp, here you go. Feel free to be brutally honest. I can take it. <3
Something or someone watches me, hidden by the suffocating darkness. I can feel it. That’s the worst part, knowing they are there, yet unable to find the eyes in the far reaches of my mind.
This has a lot of potential - it's creepy and intriguing.
I think "someone is watching me" would be more powerful. "something or someone" takes the reader away from the immediateness of the situation. Chase's suggested edit is definitely something to consider, but for me I think "someone" is enough. If it turns out to be a non-human, I wouldn't question it (sentient robots, predatory animals, supernatural beings, etc, could all be "someone"). I like the intrigue that you don't know what's watching him - that makes it super creepy and is a great hook. The reason why "is watching" is more powerful than "watches" is that "is watching" implies it's happening right now, while "watches" could be right now, or it could be a regular occurrence, e.g. "the guard watches the prisoners" versus "the guard is watching the prisoners" - first one implies it's the guard's job, the second it's happening right now.
"suffocating darkness" - I think I know what you're getting at - that total darkness that seems like it's right there in your face, almost solid, because you literally can't see a single thing - but suffocating implies something's stopping the character from being able to breathe easily. I also agree with woollybear that you can use more words to describe/expand it. I'm already hooked that someone's watching the character.
I like the short second sentence and the first part of the 3rd sentence. I'm not sure what the last bit of the 3rd sentence means. Is the character psychic, literally searching for whoever's watching them, using psychic abilities? Or is it referring to them thinking about who or what might be watching them? I think that needs to be clearer. Again, don't feel rushed to get too much into the first three sentences. Your hook's in the first sentence so you have room (so to speak) to expand on that a little. It's important that the situation is clear - the reader won't know what the character doesn't know, i.e. who or what is watching them, so you're can make the immediate situation (what the character does know) completely clear without spoiling the intrigue.
I'd read on at the hook in the first line. Whether the confusion of the 3rd line kicks me out of the story or not probably would depend on what mood I'm in and how much I want to read the book (as opposed to just randomly picking it up in a bookshop because it's there).