Napoli shouldn't be worried about just having this loss, things happen and as long as they can recover from this then there won't be too much of a problem and they should be handling it without much problem. I understand that it may look like it's a bigger deal, but in reality it is not really that much of a big deal at all, we need to remember how this could be a very normal situation without a doubt.
So, I believe we are overreacting whenever we are saying this could be normal, and we should just move on with this without much issues. I believe Napoli will have a shot at the title, this loss won't be the thing that makes them lose it, they will still have a chance to win it no matter what happened in this game.
Napoli should take lessons from the defeat, even though their opponent was Lazio. They missed the first place and now they have to wait for Atalanta defeat to jump in front of them. The problem is that Atalanta recovered very well after the weak start and they look like unstoppable right now. Their defeat against Real Madrid shouldn't affect them since they did quite well and scored two goals which is good in my opinion.