Yes, feeling weak and also feeling hot/warm can be a sign of die off. But other people can get completely different symptoms of die off, and weekness/feeling hot can be signs of something else entirely... so mother nature just does not make these little hints very clear unfortunately!
As for things to help reduce diet off symptoms, I've heard that extra water, doing mild vinegar enemas, or taking vitamin C can help. Do a search on this forum for NAC, and you'll see some posts where people are trying NAC for die off.