My 18 yr old cat throat was little swollen,from bad thyroid,and it could be from chemicals she or he lick off their fur,from places was cleaned or sprayed..she had big appetite, watery diarrhea and died five months later.vet didn't do much to stop diarrhea,but I think it could of been bacterial over growth in the stomache also.i wish vet helped her more.
Off the top of my head, it could be an infected gland, or some illness (many treatable) affecting the thyroid, or a non malignant mass.
Any of these could be affecting appetite/weight.
In other words, don't panic yet. Wait until the tests are done before assuming the worst. Did the vet give you any instructions for at home care?