Why IM particularly? I've heard of ketamine being readily absorbed through mucous membranes (mouth, nose, rectum), or injected intravenously, but never an IM shot. Is what you've got a veterinary preparation or something? (No idea if that's different from regular ketamine, I just can imagine a vet using an IM injection for a smallish animal that can't readily take an IV.)
The risks of ketamine are vomiting and a spike in blood pressure that could lead to a stroke. Also you'll be seeing some shit. I took it as a last-ditch depression treatment, and I found the hallucinations terrifying. Kind of like being in a not-fun version of Disney's Haunted Mansion.
In general, I don't trust poisoning/OD'ing. I've seen stats like twenty failed attempts for every successful one. Still, some people are averse to the more violent methods, and I can see why.
I know that ketamine can temporarily relieve the symptoms of depression, and if you actually have K, it might be worthwhile to try a non-lethal dose to see what it does for you.