I also had a small black dot on my tongue. it was the size of a pin head. it's gone today. i don't smoke, drink, use drugs nor have i been ill.?

It's gone: That is probably the key - that it's gone. Bad things don't come and go. They usually just get bigger or more painful. If it returns and gets bigger then you should see your family doctor.

Hard to say: If you're not having any symptoms now, it's hard to say what may have caused your symptom. It could have been some trauma or something you ate/drank, or something that came into contact with your tongue.