I am a player of Diamond and Pearl and last week I made a new account and just because a Drowzee is awesome, I wanted to catch him. But I don't know if it's possible and if it is, where do I find him and how?
Yes, it is possible to catch Drowzee in Pokemon Diamond/Pearl.
You can catch it on Route 215 during a Swarm.
Hope this helps!
More info on Swarms here