>My biggest issues now are significant decreasing in comprehension and
ability to retain information (stress/ sleep deprivation and health
issue). I have to read very slowly and sometimes re-read same paragraph
again and again to get the idea even if it’s basic. Or if i do
understand what i just read, it basically just fly out of my head when i
turn the page.

1. If your mind is distracted by other things while you're reading then you're likely to be reading the words at a superficial level without taking on the meaning of those words. You're not retaining that information because you're only reading the words at a surface level. This can happen to anyone. The only "cure" is to either "resolve" the things that you're worrying about so that you have time to read without distraction, or find a time to read that allows you to give yourself a break from all your worries during that time.
2. If you're having difficulty with comprehension because you're reading in English and English is not your native language, then it might help to read some easier books (in a more relaxed way, i.e. without having to think so hard) and gradually increase the difficulty level of the books you're reading. Or have a dictionary on hand, so that you're not relying so much on your intuition and trying to piece together the meaning of a sentence when you encounter a word you're unfamiliar with.
3. Some books are more engaging than others. If you find you can't "get into" a book and you keep re-reading the same paragraphs because the book seems boring and it's failing to draw you in. Pick up a different book. Return to that book, if you want to, at a later time, at which point you might find yourself getting into it without having to try.