Eli Roth hosting the TMZ "After Dark" tour might sound like a dream ... but, it really happened Friday -- on the same day his new movie opened in theaters.

The director and actor jumped on the bus to show fans around Los Angeles ... and, gave them an inside scoop on "Dream Eater" -- by far the scariest movie of the year -- which Roth also happened to produce. TMZ.com

It's a found footage flick -- think "Paranormal Activity" and "The Blair Witch Project" -- that touches on sleepwalking ... which Roth says he can kinda relate to since he used to get horrible sleep paralysis and night terrors.

It sounds like Roth's dealt with a lot of horror movies come to life BTW ... 'cause he told our audience on the bus about the haunted apartment he lived in while making "Cabin Fever" during the

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