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Hello. I'm sorry to hear about your situation.
Unfortunately, there is no way to humanely euthanize at home. The only humane option is by giving an injection of Euthanasia Solution (sodium pentobarb) IV. If you give a sedative, like Lorazepam, he'll either end up a bit sleepy or he'll have an adverse reaction and be agitated and over-active. That's what happens when we overdose these valium type drugs in cats.
The only other approved at home euthanasia, is a well placed gunshot wound to the brain. I would never recommend somebody shoot their own cat, but that's the only other option. Any other pharmaceutical option will lead to suffering for hours or days before the cat dies.
I'm sorry again for this situation, but I'm afraid there is really nothing you can do other than finding a vet to do the euthanasia.