I've always lived with cats. My two eldest cats are 15 and 13. Ive had both since they were kittens. My 13 year old is Lemon. We have been best friends since we first met. Im 18, and ive grown up with her. She's never shown any aggression towards me. Ever. Lately, (since on a diet) shes been acting more energetic. But the past few days, shes peed on my clothes (not uncommon for her) and today she got a bit upset that i wasnt petting her at the moment and hissed lightly. She's never done this and i dont understand why she did. Im worried about her and if anyone can help me understand that would help so much.