My 5.5 month old had been a champion sleeper until last week. She had been taking 2-3 naps (~1 hour each) with no problem, and sleeping 7:30pm-7am with no wakeups in her own room. She had a cold early last week and even though she's now totally healthy it's like she forgot how to sleep! Falling asleep hasn't been much problem - but then she has woken up every night around 2 or 3 am and been up for 2-3 hours at a time, fussing the whole time. It's like she startles herself awake and she's forgotten how to settle herself down. We give her at least 10 minutes to try to self-soothe before checking on her. Changing her diaper, nursing, rubbing her belly - they all comfort her for a minute but as soon as we leave the room she fusses again. We have no issue letting her cry it out after we make sure her needs are met but even so, it has taken her hours to finally settle. She's perfectly content when she's awake and doesn't seem to be in pain. Any advice on a sleep training method??