When you are very high on a dissociative anaesthetic drug (ketamine, pcp, dextromethorphan, others), you are either unable to move, or forget that you CAN move. Thus, you are stuck.
This term applies only to dissociative
drugs, using the term in reference to the high of any other
drugs is improper.
You
don't get stuck on marijuana, your just too stoned. The
people that say this for marijuana or other drugs would stop using it in reference to those drugs, if they ever actually had the experience of being truly "stuck," on dissociatives.