I have no idea how to read this. I thought it was saying to do something like /somnia fatigue set 1aaron5 100, which didn't work, so I tried going down to /somnia fatigue set 1aaron5, which said Invalid Double, so I tried /somnia fatigue set 1aaron5 100.00 which also didn't work.

I just found the wiki page for it, but in-game would very helpful

Also, hitting tab after /somnia fatigue set puts my player name, rather than an amount