Collective unconsciousness
Collective unconsciousness was a theorized state of mind, explained as essentially an unconscious variant of the Collective consciousness that existed in for example the Borg.

In 2374, the crew of the  encountered a Delta Quadrant species whose reality was a shared dream, linked together by a neurogenic field. Upon the beings inducing somnolence in the Voyager crew using a neurogenic transmitter, the crew found themselves in what became clear was a shared dream, they theorized that this was made possible by inducing a state of collective unconsciousness. ()

See also 
 Communal dream

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Medical conditions