strange disorder

Hi,Iam just comming across a peculiar syndrome where the elderly patient is very comfortable in bed, but the moment we attempt to get him out of bed he has panic attacks, even if we manage to get him out into a chair he doesnt even last for 2 minutes, he tends to extend his knees & slide down from chair and totally destabilses himself,Iam not sure if its is decorticate rigidity as i was taught decorticate rigidity would be quite sustained whereas this patient has this episode only when we attempt him to get out of bed.
Thanks in advance