1)
Do they not sleep if they do not do evil?
1.
Rashi: Yes - they are unable to sleep.
2.
Malbim: Yes - if they do not do evil, they do not sleep at all.
2)
Why does it add "v'Nigzelah Shenasam Im Lo Yachshilu"?
1.
Malbim: If they themselves do evil, but do not make others stumble, they sleep, but it seems that their sleep is stolen. They think that it is not proper to sleep until they also make others stumble. This refers to Ra'im, like heretics and Apikorosim.
