Not a Tohatsu expert so my advise and information is generic small engine
Most small engines get their spark from a magneto which generates a pretty good jolt. The kill switch grounds the magneto to the engine so no spark and the engine stops.
Sounds like you have either a bad connection between the kill switch and the engine block or a short between the hot wire to the switch and the switch body. Most likely I think is the first.
Check the wire from the switch to the block carefully for broken or frayed wires, loose or corroded connections either in the switch or at the block. Then check the wire from the magneto to the switch to make sure it's well connected, no broken insulation
The good news is it probably
won't kill you although if I had a bad heart I would be careful.
However, as you noticed, it can give you a pretty good jolt. Maybe a way to give up that morning coffee habit.