What Causes Insomnia After Taking Ativan?

I have been recently switched from 1 mg xanax at bedtime, and 1 mg. in the middle of the night (T. 2mg per night), for chronic severe insomnia, anxiety related, to one mg. Ativan at bedtime, and no second dose. The MD said ativan is longer-lasting. Quite the contrary! I remained wired, and didn't sleep a wink! Could this be a paradoxical reaction, or is this dose much smaller comparatively to the xanax? Also the pamphlet accompanying the ativan had MANY more precautions and possible side effects than the one for xanax, including memory loss, rapid heart beat, etc. Which greatly concerns me! Please advise.