The LD50 dose for CN- is around 1-3 mg per kilogram. And yes it's probably going to be painful.
There is a source of doubtable claim out there that Cyanide has a 97% chance of killing you but ranks 51/100 points for suffering.
However, it's possible to treat CN- poisoning. By using NO2-, we can create a similar effect like with SN poisoning methemoglobin which the CN- now create cyanmethemoglobin which can then be treated with methyl blue to make your body able to carry O2 again.
There are others like S2O3 2- which is used in the US. Or Hydroxocobalamin (Vitamin 12) which can be used to form cyanocobalamin to neutralize your CN-. However, other countries like for example Ireland does not have a standard anti CN- kit anymore.
The only upside I see is that CN- is very easily obtainable, although our labs contain almost all Suicide affinity salts like SN, SA or in this case CN.