While tylenol (paracetamol/acetaminophen) is probably one of the safest drugs around when taken as directed. In fact, it's a drug often recommended for people with significant liver disease.
Howver, it is a serious danger in overdose, and is the most common cause of non-accidental poisoning in much of Europe.
It's possible for as little as 6 -8 tablets taken over a few hours to cause serious or fatal injury, particularly if you are a regular heavy drinker (more than 20 beers, or a bottle of spirits a week).
5 tablets is unlikely to hurt, if you are otherwise fit and healthy and don't drink regularly - just don't take ANY more for at least 24 - 48 hours, and don't do it again.