DId your physician tell you why he cut your dose fro 45 to 22.5? Did you have lab work that was out of normal range?
It can make you to drowsy during the day, were you having any problems with that? Also I do not know what other drugs your on?
Could it be the cause of your insomnia, I am not a professional but I would suspect it may cause your problem.
Please call you physician and clarify why he changed the dose.
Take care and keep posting.