I was once given Reglan at the hospital for nausea. Within three minutes I was sitting up rocking in the bed, crying, sweating, screaming at my Mom that I hated her for dragging me to the hospital, trying to pull out the IV and basically losing my mind. It was the worst feeling of anxiety and anger I ever had, and I could have clawed my skin off I was so suddenly hot.
The nurse took a look at me and saw my poor Mom holding my hands so I didn't pull out the IV. She asked 'should she be really hot right now?' ('F-you I'm not hot I'm done with this ER! I'm LEAVING!') the nurse shook his head and said 'I will get the doctor with some benadryl.' (I cursed at the nurse for good measure, since by then I had moved from yelling at my mom to my poor boyfriend that was with me at the time). By this time I was rocking so hard everyone was staring at me (i was in the hall at the ER b/c there were no more curtained areas left - don't got to the ER on a Friday night) and getting obviously concerned for their safety - I must have looked that scary, plus I'm the daughter of a trucker, so I learned some good curses, all of which I was yelling about the 6 hour wait to get a scan.
The doctor came over, injected the benadryl and I was almost immediately better. He told me it happens when Reglan is pushed too quickly into the patient, or sometimes just because. He said they've had people just stand up and take the IV pole with them out the ER. I apologized to everyone, and they were cool with it, thankfully. I'm not the type to yell at nurses, they're so under appreciated.
My point of the story? It is very easy to give the drug like that on purpose (and the nurse joked they do it to the 'people we want to get rid of') and get such a reaction. I could have easily hurt myself to get off that bed, and I'm lucky my mom was willing to basically sit on me holding my hands until help came. I wouldn't give that drug to my worst enemy.
That said, imagine if you locked someone in a room and kept giving them that? They'd hurt themselves to get out, and be crazy anxious and angry at the same time.
And prolonged use of the drug can cause major life changing damage too. So there's that.