5mth old waking an hour after I put him down?!

[Poshers]

Basically 5 Month old waking up crying hysterically an hour after I've put him down at 7pm in the evening. He's done this the last 3 nights out of the blue! Any tips? Reasons why?

My daughter sometimes does this about 45 mins after she's gone to sleep at night. It's probably due to transitioning through a sleep cycle. We have a video baby monitor and if I can see her eyes are closed I leave her and she gets herself back to sleep after a few minutes of crying. She often cries going to sleep in the first place do we are fairly immune to it now!