Waking in the night but nothing wanted- at all!

[jjazz]

My DS has been waking in the night for a couple of months or so now- he is 20 months and (other than very early waking during the summer months)- he has been a good sleeper. He goes in the cot awake and settles well in the evening. In the night- usually around 4am (ish) he crys loudly and is usually standing up. On going in he is awake but instantly calm. He lets me lie him down and lies quietly. I tuck him up without talking or light etc and I usually hear no more. On a bad night I am just about dropping off to sleep again and 30 -60mins or so later he does the same thing all over again. Knackering. He usually settles for the rest of the night after the second or third time of settling. He can then wake for the day at 6.30 ish and have a happy jolly day- no signs of sleep deprivation for him- only me. He is a good (ish) napper -approx 1 hr- 1.30 around lunch time so I dont think he is in need of more day sleep.
Any stories from mumsnetters who have tackled this and /or just lived to tell the tale would do!