What are the symptoms of insulin overdose?

You’ll start shaking and sweating, dizziness, confusion, irritability, rapid heartbeat, blurred vision. That’s just mild overdose. 

If it’s severe overdose, coma or death. 

Hypoglycemia, low blood sugar. If you are not sure, simply test your glucose levels before you take the insulin. But hypoglycemia can be fatal.  You need to set up an accounting system for your doses, a chart, a list a book whatever.

Extremely low sugar.
Fainting and coma.