MotoGP champ Marc Marquez is VERY fortunate to be alive ... he just crashed during a practice run Friday -- and the scene was HORRIFYING.
The 28-year-old was heading around a turn at a high rate of speed during preparation for this weekend's Dutch TT in Assen ... when all of a sudden his bike bucked him.
Footage from the track is absolutely terrifying ... you can see Marquez was thrown feet into the air while his motorcycle skidded across the pavement underneath him.