Anxious cat

[AverageJoan]

Hi all
I have an indoor cat who is 2 years old and he's always been quite anxious - hates going to the vets and hisses when I try put him in the carrier etc, he can be very aggressive.
We had family over this weekend to stay and he was absolutely fine with everyone (staying out of the way but not confrontational) until this morning when seemingly for no reason he just started attacking anyone walking past or near him, including myself as he batted me and hissed when I was sat next to him after he'd just let me stroke him. He's drawn blood from SILs ankle.
Is there anything we can do to calm him down, I'm not even sure what could've caused it. Everyone has gone now and he seems fine again but I don't really want it to be a thing every time people come over. Thanks in advance

Feliway do a plug in? He was obviously overwhelmed by so many people. Poor kitty.

I should also mention that he isn't normally aggressive, just that he can be sometimes such as going to the vets. Normally he is quite friendly and comes for occasional cuddles, though not a lap cat by any stretch.

Feliway plug ins never worked for my cat. There's a very natural medication called Zylkene. You can get it on Amazon. It's only made from milk protein and you just crumble it in to their food. It tastes milky so not unappealing to cats. It's the ONLY thing that works in calming down my anxious cat. When we moved house he had a full on nervous breakdown but was so much calmer after 2 days on Zylkene. I just give it to him during times of stress such as us going away, guests staying, fireworks etc.

Thanks for your reply, I've tried these before when we brought a new kitten home and it didn't seem to work for that purpose though they get on fine now but may be worth trying if we do have people over again! He definitely wasn't happy today but it was just shocking as he's been fine all weekend and it seemed something just triggered earlier

Thanks for this! I'll definitely check it out. He does like milk (although he's never allowed it) so I'm sure he'd probably like these.

Feliway optimum works better than standard feliway, I noticed it helped our most recent cat when standard feliway didn't seem to. Also making sure he has his own safe space where he won't be disturbed and the ability to get up high to escape situations if he wants to. Playing with toys with him can help to de stress them too.

I have found Royal Canin Calm biscuits have really helped my cat, she was stress weeing and on high alert due to what we now know is a fox visiting our garden, within a couple of days of feeding her these biscuits she has really calmed down.

This is what it says on the packaging:

Contains hydrolysed milk protein and L-tryptophan to help manage cats prone to behaviour changes in unusual environments and situations

He's clearly very stressed that his territory had been so thoroughly invaded.

Can I ask - is there a reason why is he an indoor cat?

Thanks @Stickytreacle and @unknownorigins. I did only try the regular feliway so might be worth looking into getting the stronger one! and changing the food is a great suggestion too. They already eat the indoor cat Royal Canin mix so I'll check this out too.