According to good old Medline, sleeplessness is a known possible side effect of herceptin.
http://www.nlm.nih.gov/medlineplus/d...r/a699019.html
I am semi-menopausal (seem to get a period about every few months) and the sleeplessness seems to be worse right after I get my herceptin and used to let up towards the end of the three-week period (not any more though). Although I have some stress, the sleeplessness doesn't seem to let up when the stress decreases.