Most people have a hard times sleeping when they take clen....so you may not get a lot of help with this one.
It may be one of those things like caffeine....for most it's a stimulate but there are those out there that it actually levels and calms them down....kind of goes back to the everyone is differant kind of thing.
Sorry, I know I wasn't much help with this one
there were some studies done in animals (rats if I remeber right) where it was determined to be a dose dependant forbrain phenomena. Basically the effects outside of bronchodilation are dose dependant---ie the higher the dose, the more likely the nervousness. (that was kind of a nobrainer if you ask me)
Also an individual can "overload" themselves. This happens with me with caffiene. I drink one or two cups of coffee, I wake up. I drink 4 in a short period of time, I'm wired. I drink a pot, I get a headache and have to fight sleep or I just go to sleep.