If your cat is purposefully avoiding you, hiding more than usual, or leaving the room when you enter, they might be upset about something.
An upset cat might hiss, swat, or growl when approached.
A sudden loss of appetite can be a sign of distress.
Excessive grooming, leading to bald patches, might indicate stress.
Suddenly refusing to use the litter box or having "accidents" can be a sign of upset.
Constant meowing or yowling might indicate discomfort.
If they're suddenly scratching furniture more than usual, it might be a sign of distress.
A rigid tail, flattened ears, or dilated pupils can indicate that your cat is upset.