should i be worried about my cat's potruding third lid?

my cat has a protruding third lid and i'm really worried about him. i've found so much information online and they all give different information at varying degrees so i don't know if this is something i should be worried about. i'd really appreciate any help or advice you guys have. i noticed his visible lid around 3 days ago. here's a picture of his eye i took recently. it looks scary and i get even more concerned when i can see the pink fleshy part of his lid. this one was taken a few hours before and it doesn't look so bad, but it's still very visible. he's never had this issue before, i'm thinking it's some sort of allergy or maybe bacterial infection. my house had just fostered two kittens who also had the protruding third lid. i believe my roommate gave them some vitamins or something that helped the lid retract a little bit, but i don't know the details of this process. we got no detailed information about what was causing their lid to be visible. my cat is around 2 years old. he seems to be behaving normally from what i've observed. he ate just this morning with my other cat, i don't believe his feces or urine look abnormal. ugh, but it just looks so uncomfortable and painful and i want to help him asap!! if any of you could give me some recommendations on how i can treat him, if i should be worried, etc, i'd be so appreciative!

Hello!  To fill in the background, cats have three 'eyelids,' the top and bottom one like ours and a 'third eyelid,' which comes across from the inner corner, inside the other two and helping to distribute the tear film.   Often when a cat is 'off-colour' for example with a virus, the third eyelids close partway across the eye.  However sometimes only one eyelid part closes, which suggests a difference between the two sides.  Perhaps this is down to damage to the nerve controlling the eyelid, or an abnormality to one side of the face.  This could be for some grisley reason (perhaps a lump or infection infringing on the nerve, a scratch to the cornea etc) or something more innocuous, and the outcome / treatment will reflect that. We therefore would advise contacting your vet - or, as it Bank Holiday Sunday, your emergency vet for phone triage, as they may well need to see you sooner.  Best of luck and please let us know what is found.