Here's my successful Map29 nightmare run as well. The biggest thing that helped was knowing when to use either the BFG or plasma rifle as the BFG can eat up ammo in situations that might only need a few plasma shots to get by.
Back to the original topic of this thread however, I do think Dead Simple's stair trigger may sometimes be glitched as in Ultraviolence co-op they failed to lower after every enemy was killed. Luckily its a short level so a quick retry worked.