Certainly. It's also possible for people to behave normally most of the time and then suddenly freak out as if they went off their meds. Of course, that doesn't necessarily mean they have joined the club.

The thing that makes a troll is the intent to cause problems, arguments, disorder, and the like, or an unwillingness to control oneself when discussing a topic. A person who has a bad day and posts something weird or grumpy isn't necessarily a troll. A person who consistently tries to annoy other users, or who posts consistently in a way that annoys other users after being politely requested to stop and to initiate self-control--that's a troll.