DD has always been a fab sleeper, from 2 weeks old she would sleep from dream feed through to 7am but the last week she has been waking up anytime from midnight to 3am then again every hour right through to morning, room temperature is fine, nappy ok etc. She wakes up and chats to herself which I ignore hoping she'll settle, this turns into a cry after a few mins, I give her a dummy and she goes back off to sleep for a hour, then stirs again, dummy & back to sleep again. This carries on until getting up time. Before the last week she'd self soothe, wake, chat, suck thumb, sleep again but only occasionally, typically she'd sleep all the way through without a peep. She seems to have forgotten how to self soothe.
Hi super my DD1 did this at 5 months. She'd been a fab sleeper until then too, and we were totally thrown off balance. Sleep deprivation is a killer! She had another dodgy patch around 18 months but now (30 months) sleeps a reliable 12 hours a night.
No tips really, other than the faithful 'it's a phase and will pass', although I know that's not much comfort when you're in the middle of one of these phases! DD2 (10 weeks) isn't sleeping through yet, so I feel your pain, but hang in there and your DD will work through it and be self-soothing back to sleep before you know it.