I found this on a box of non-prescription tablets:
The way I read that, the commas make the phrase “half an hour before going to bed” parenthetical, so you are advised to go into a darkened room to take the tablet. After that, presumably you can switch the lights back on to go to sleep.
There’s probably some neat pun on “comma” and “coma”, too, but I can’t think of one right now.
don't confuse the narrator 