Night wakings

My 6 month old was sleeping really well, 9-10 hour stretches, and when he woke would go right back down after I nursed him. Lately he has been waking several times in the night and is upset and difficult to put down- sometimes doesn't even want to nurse and just cries! I'm wondering how to handle these wakings- I want to comfort him but also don't want to start any bad habits! Anyone experiencing the same or have advice?