Help: 8yr old cat - Sudden Head Tremors

Tonight I noticed my 8 yr old cat, Brady's, head shaking and his eyes were dilated. I have never seen his head tremor before tonight, and I'm terrified! Does anyone else have experience with head tremors? I made an appointment at the vet first thing in the morning, but until then, I could use some peace of mind and hopefully some answers from any of you that have experienced something similar with your cat. The only thing that has been different is a places a Seresto flea collar on him about three weeks ago. I removed it tonight as soon as I witnessed his head shaking. Any advice or comfort is appreciated.

Head "shaking" and/or "tremors" is kind of a vague description, could mean anything, so for real peace of mind, you should consider calling an ER vet for direction - they can tell you whether this can or cannot wait until tomorrow.  Also concerning is the dilated pupils, anytime the pupils are dilated and accompanied with another health issue, is cause for concern and direct veterinary advice/supervision.

Please, do not ever use flea collars on pets.  The seresto in particular allegedly "provides protection for 8 months", imagine for a moment the continued exposure to that against the skin (potential for skin absorption) - also, commercial flea collars almost always contain substances that are carcinogenic.

Please call an ER clinic ASAP, describe what you saw in detail, they'll advise you further.

The well known feline vet, Jean Hofve, published an article by Dr. Michael Fox (www.drfoxvet.com) about the dangers of pesticides being used on our companion animals, and I would recommend it for anyone who owns a cat or a dog.  You were wise to take the collar off.  It is mentioned in the article, and both chemicals it contains can cause seizures.  http://www.littlebigcat.com/blog/flea-and-tick-product-dangers/

It is a long article, but if you skip to the end, there are 11 comments posted at the bottom and all have to do with the Seresto collars.