Well I'd imagine suddenly having behavoirs and dreams like a wolf, which I beleived was discussed about with what happens before the first shift, would make something think they're crazy. So someone that may be 'weaker' may give out during that time. The painful shifting process, not knowing whats heppening, and becoming some beast may in turn may that person go crazy too, it seems to matter on how they behave to such situations, yet I think even the calmest and most serious person would be screaming (and soon howling.) during and after a shift.
If the person had figured out what they are, then they could expect themselves to be blood thristy monsters and their mind could get the best of them, causing to become and beleive what they've only heard of through stories.
Though the above is is if the person had not really beleived they exsist, though even a beleiver may very well freak out. Though mainly because they don't know what the hell is happening to them. So if the werewolf who had bit them, or was preparing to do so, would probally tell him what was going to happen, what it is, what it isn't, and then prepare them for their The First Shift. (We all love The First Shift now don't we? That is not talking about work shifts.)
So a knowledged werewolf could still go crazy. If they did not want to be bitten and then learned everything from another werewolf, they could be very upset from the stress of it. A person who had agreed to but was just bitten may have second thoughts. Then they have to go through the trouble that may lay ahead of them, how ever the extent it may be.
A werewolf tired of keeping his secret may be stressed too. Or if say someone saw the werewolf shifting or in gestalt and runs around claiming werewolves are true, though most people would scoff at the person who had seen the werewolf, that could still be stressful.
Other than that I think alot of werewolves could get stressed or pissed from alot of other things a regular human would really dislike.
werewolf tossing 
at everyone? 
