Hope this explanation is relevant
[b] A similar pseudo-passive is used with verbs of posture:
Grandfather was sat in the rocking chair.
I've been stood here for about ten minutes.
In this case,the construction is largely synonymous with,though less common than,the progressive construction: was sitting, have been standing, etc.
Source: A Comprehensive Grammar of the English Language by Quirk et al. P.170
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