Welcome back to the community @harrydodgson,
Sleep and Power Off are two different features. If you let EMO sleep, it means he is still powered on. However, if you power him off, he is no longer active, and there is no way he could fall onto his right side as you described.
Actually, it’s a known issue…when EMO is busy doing anything, like daily activities, singing, dancing, and playing games, his optical foot sensor is automatically temporarily disabled.
IMHO, I will never trust this sensor 100%, particularly when it is unattended on the table… Provide an enclosed play area for him… so EMO can walk safely and not fall off the table.
Please click on the link below for information and instructions…
Pls. Click Here!
GOOD LUCK, BEST REGARDS, AND TAKE CARE EMO!