Cat got hit on the head

Hi my cat hit her head she's very active and playful but she started to sleep a lot and she doesn't seem to want to be with my other cats she's isolating herself and when my other cat that she used to play with a lot come to her she moves and hisses. I pick her up and she meows like she's in pain

Hello;  your poor cat.  I have no sense of time-scale here.  Was this today, or some time ago?  How did your cat get hit on the head?  Are we talking about a road traffic accident, running headlong into something or something else?  At any rate, you'll know that a head injury is an emergency, as is that level of pain.  If you haven't yet sought this, please do so now.  Cats usually avoid showing pain but it sounds as if your cat is obviously uncomfortable, to the point that they can't really hide it.  This animal needs to see a vet - and quickly.

It happened 2 days ago and she fell off the cat tree but i’ve never seen her so isolated and lethargic. I’m not sure if she’s in pain i feel like she’s sort of confused she doesn’t want to play with my other cats but she used to be the most active

And there’s no dilation in her pupils nor vomiting or any sign of sickness that’s why I’m confused

Hi - it's ok not to know the answer at this point.  I have a head injury and have never circled or flicked my eyes (nystagmus) either.  There is a massive range of flavours of head injury and no one symptom that can rule a brain injury out by its absence.     However, there are many other medical possibilities including anaemia, liver or kidney disease, low blood sugar, internal bleeding (the fall from the tree could be a symptom as well as a cause).  Pain cause cause a huge range of symptoms in itself.  I would strongly advocate having this one to the vets, communicating the symptoms and letting them do the tests to find the cause of this change.  They may triage the case for you because some problems presenting with these symptoms might well might turn out to be an emergency.  Triage is the process of making sure that the appointment time you have been given is appropriate.