Probably the windows key, alt/fn key, or a special function key the manufacturer put on there somewhere. It's also an option in the keyboard&mice section of the control panel.
I got it for back pain (the baclofen). I have constant pain in my lower back, shoulders, and knees. I suspect from repeated lyme (degenerative muscle disease) and doing some pretty intense sports back in the day. Now I just climb rocks n shit. :D
Anyway, yeah, shit knocked me out cold... Granted I took 60mg (read somewhere on BL 30-60mg was recreational as I didn't expect shit given that I take opiates to self-manage pain) and wham. Couldn't keep my eyes open.