It's less harmful than alcohol and cigarettes despite its legal status, but it is a terrible habit. The most dangerous thing about it is that it affects people without them knowing... you may feel like it's all just fun and harmless, but in reality it is holding you back (making you dull, lazy and less motivated). I wouldn't recommend doing it more than a few times, definitely not as a daily/weekly habit.
It depends on the strain that you smoke. Most likely you were smoking Cannibus Indica this type of Marijuana is produces much more flower then Cannibas Sativa.
Cannibus Sativa is the one that give you more of a head high and does not affect your body much. It does not put you to sleep and actually makes you more energetic.