This happens to us approx every 3 months or so! Just when things are going good then wham another few weeks of being unsettled when it's sleep time and needing that extra comfort. Sometimes it's as simple as just staying by her cot, she just needs the reassurance that we are there for her. We definitely went through it big time around 4 months, 7/8 months, 11 months and are just cruising out of another patch of it. The fact that it does pass it what gets us through it.

Like MadB we find it settles quicker if we help her through it. Good luck and hope everything settles soon