yes it is harmful to mix tussoinex with water due to the combination of drugs that are there. there is a higher chance of overdosing yourself with it one of the symptoms of overdose is nausea
, severe dizziness
, severe drowsiness
i would suggest you visit a hospital to rule you out of an overdose preferably you are taken by someone because it is not good to drive when you have taken an overdose
hope have helped in answering your query
get well soon.