Is it normal to have destructive sexual fantasies?

Nearly everytime I masturbate (5-15 times a day) I use my imagination to feel like im being fed into a wood chipper or being eatin by a monster. Sometimes ill imagine being morphed into inanimiate objects (usually against my will) like in Ernest Scared Stupid with the wood dolls. The thought of being totally destroyed, transformed or digested is a powerful enough turn on to where i rarely consider usual sexual thoughts for assistance. Is this normal?