I know I've mentioned this before in other posts. In retrospect, I suppose this counts as chemical restraint (not a traditional one), though I still have no idea why they did it. It was my first time going inpatient for bipolar depression. There were the usual depressive symptoms plus a certain amount of agitation. I was jittery, nervous and feeling like I was jumping out of my skin, but not hostile. Still, they felt it necessary to hand me a cup with a whopping dose of Klonopin (Ativan? Some sort of benzo.) and told me to take it with an intimation of "Or else." when I asked questions.
I came back to awareness nearly a full day later eating lunch. Wasn't in any four point restraints. The other patients said I hadn't caused a ruckus. I was agitated, sure, but not agitated enough to be drugged into another world because they just didn't want to deal with me. That's the only reason I can think of and that still doesn't answer the question why?