Might be an episode of The Outer Limits, "Counterweight". Wikipedia description (spoilers):
Four scientists, a newspaper man and a construction tycoon agree to
spend 261 days in isolation in an interstellar flight simulation to
planet Antheon, a world that would be a potential target for future
human colonization. But the experiment is secretly infiltrated by an
extraterrestrial presence, who causes the subconscious mind of the
various passengers to go amok: one of the passengers finds the doll of
his deceased daughter on his bed, while another one is almost choked
in his sleep by invisible hands. As months pass onboard, relations
between passengers become increasingly tense and uneasy, each one
being faced with his own part of darkness. Horror eventually escalates
with the plants of one passenger coming to life and destroying one
another and the presence incarnating itself into one of the plants and
making it grow into a huge, hideous creature. The extraterrestrial
mind eventually reveals itself to the entire crew, claiming to be one
of Antheon's indigenous inhabitants. The Humans are accused of
planning to come to Antheon with intentions of aggressive
colonization, one thing the aliens cannot accept. In the end, the
simulation is interrupted.
You can also watch it on archive.org:
http://archive.org/details/TheOuterLimits-Tos-2x14-Counterweight
