Please can someone advise

Hello All
I new to this group,and have found a lot of the information on here
very helpfully and has given me something to think about,
I have three cats two male and one female
one of the male cats Silvester is not well at the moment he has been
sick twice yesterday and today ( that i know of ) which is green and
he lets out a cry just before
the weather has been very hot here in the UK these lasts few day up in
the 90 F great for some us humans but not if you're wearing a fur coat
all day G
I will be taking Silvester to the vets hopefully tomorrow but I
wondered if anyone here has any ideas what could be the matter he is
off his food and not drinking either which I find very worry in this
weather, He is asleep at the moment in his favorite room and I have
the electric fan on which is keeping the room cool

martina