My cat Smokey..this morning...walking slowly around crying.then hed stumble.then he layed down.this kept up for a bit,.i tried feeding him and giving him water he just cried.i picked him up for a bit holding him.i called numerous vets..they wouldnt check him due to them not taking payments/and wanting money up front(which varied from 40-75),this i didnt have, i cuddled wwith him,.he layed on the windowsill nad was looking and acting better..but panting and clear liquid was coming out of his mouth. then he started shaking.i pet him he stopped..it was on and off.then he was crying and still shaking..but not moving much.then he started gasping and trying to breath ,still shaking.then he went stiff. he was a great cat , i would like to know if anyone knows the symptoms that killed my beloved cat and if they are associated with anything.

smokey was 1 1/2 years old, an indoor cat.not nuetered,and wearing a flea collar. thanks in advance.