Hi Renee, and welcome!
I'm sorry Cat isn't looking/acting like himself.
From your description, it's possible that he has a neurological disorder called Vestibular Syndrome. The vestibular system is inside the ears and an ear infection, ear mites or debris in the ear can be a cause of this. Here is more information:
While it's possible that there IS a foreign object in his ear, like a bug or spider that crawled in there, it's also possible that he may have ingested something he shouldn't have and is causing his symptoms. I'm glad there's no alcohol in your home, but since you had so many people over at your party last night, it's possible that a guest fed him something he shouldn't have had, he could have ingested a human medication that fell on the floor, nibbled on a houseplant or flowers, if you have any, or perhaps there was something else accessible to him. These are just suggestions of what might possibly be causing his symptoms, as I am trying to be as helpful as possible to your Cat.
It would be advisable to have him evaluated by a vet as soon as possible, to get a definite diagnosis and treatment, so if your regular vet doesn't have emergency hours, taking him to a nearby ER vet center would be your best next step.
Continue to monitor him, keeping him in a quiet area--the room can be dimly lit, not completely dark--and don't let him jump up on anything or walk by himself, since he's dizzy and can't walk straight, until you can get him to the vet, which hopefully, will be soon.
I hope all will be well with Cat and please let me know how he's coming along and what the vet tells you. Thanks!
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