My Shadow did that too after I brought him home last March. He was here for 4 days and then it just started. He would just be laying and then hiss and growl and bite at me if I was nearby. I felt awful. I took him to vet and he was put on gabapentin for a couple weeks and then tapered off.  He has not been on it since then. But he still has these spells where he will just growl or hiss for no apparent reason. Sometimes just walking/hopping through the room, sometimes just laying on the floor, sometimes while playing (we are currently working on weight loss). The other day we were playing with 'da bird (his favorite wand toy) and he just stopped, flopped onto his side and then bit his one back foot. (He is a right front leg amputee due to non-treated fracture probably from getting caught in a trap). I only rescued him after his amputation surgery. So I know nothing about what he was like before that trauma.  I just can't tell if he is actually in pain or just irritated that he can't play like he obviously wants to. I have mentioned these episodes to the vet with no real resolution. So I thought I would pick someone else's brain.  

I also wondered if the humidity affects any one else's tripawd? He seems to be more irritable when it gets very humid. As such I have been running the central air a lot but some days even with that one he will be growly and hissy. One day he had 8 growling/hissing/seemingly irritable spells, while the AC was on. I asked at the vet's office last Saturday when I picked up his new food. The gal at the desk also has a 3-legged cat (trauma related amputation) and I asked if her cat seemed bothered by humidity and she said no. I explained about Shadow and she said "I guess he just doesn't like the heat". My sister just says "he's a cat" and "I guess he is allowed to have a bad day every now and again". So, if anyone has any suggestions I'd appreciate it. Thanks. I have not been able to catch any of these spells on video...much to my dismay.