Dr told me to use. 5 mg of ativan (lorazepam) for insomnia, but to prevent addiction or need for higher dose, take sun thru thurs & not on fri. And sat.?

For awhile maybe. Then the psychological dependency may also begin , i.e. , if you have a couple of poor nights sleep on the Ativan (lorazepam) nights and perhaps some struggling more than normal on the off nights, you may find yourself taking an extra dose on your medication nights or perhaps a dose on your off nights. At the end of the day, it's a temporary solution to a longer term problem, even taking it prn.