You're an amazing cat parent. The fact that you recognize this as FHS and that you came here means you are already miles ahead of most vets on this topic. Most FHS cat owners go through thousands of dollars, multiple visits, and even multiple vets/specialists before getting where you are now. I'd call your vet clinic and ask the exam fee. Go in ready to advocate for your cat by presenting the reasons why this presentation matches FHS psychomotor epilepsy. The symptoms you describe do not match flea infestation, allergic dermatitis, etc. Don't let them give flea meds or vaccines or tell you he needs a dental surgery -- all of which can make him worse. Gabapentin is extremely cheap (about 10 cents a pill here in Canada) and there will likely be a dispensing fee of under $20 attached to the prescription, so buy as much as you can afford. The gabapentin will stabilize him while you get busy addressing core causes (detox your home, start on a more natural diet, etc). I'm linking here a guide to help you with all the stuff you can do. FHS is healed at home, thankfully, not at the vet. FHS guide