I haven't seen any bad reactions to Panacur (and I guess you are talking about the liquid that you give 1ml per Kg of bodyweight every fortnight until they are 12 weeks old). Once they are actually around 8 weeks, Drontal seems fine, with one tablet (or part thereof) per 10Kg of bodyweight, and it is an all-round wormer, whereas the Panacur only treats against some infestations.
I have recently heard that Milbemax, another wormer which is supposed to be able to be given right from word go, does not in fact eradicate hookworm, but I don't know whether any further information on their clinical tests is available.
With young puppies, there are a lot of factors that may influence their energy-levels and activity - mostly it is what you put into them, but referring to previous posts, it can also be down to what you take out of them, and whether they are allowed their sleeping time at the right times. With yooman babies, if they are kept awake for too long, they can then become hyper .... maybe it is just a question of striking the right balance !!