9 month old sleeping sitting up?!

[AussieGirl78]

My 9 month has started sitting up and sleeping in his cot
I put him in his cot in his sleeping bag lying down,he goes to sleep and then about an hour or two later will start crying
I go in and he's sitting up asleep and startling himself
I lie him down and he goes back to sleep then in another hour or so he's sitting up again

Any ideas or suggestions gratefully accepted!

Unfortunately I have no ideas or suggestions for you, but wanted to let you know that your Ds is not the only one. My DS has been doing this for months. I've tried to settle him back in his cot each time, but the only way i can calm him is by rocking him in my arms and then trying again (although more ofen than not, he won't resettle in the cot and he ends up in my bed, or worse, sleeping on me!)
according to my HV this is something they go through when they learn how to do something new, but he's been sitting unaided for over three months and there's no sign of him stopping, the only difference is that for the last two months, if i don't get to him in time he's then pulled himself up to stand and then really won't resettle.
I'm eager for ideas and suggestions too, although i'm sure its part of my Ds's hyperactivity and unwillingness to sleep in the first place.

Hi,
If it's any consolation it IS easing off now
I'm wondering if it was somehow related to teething? But hooray for sleep!