What does on-off phenomena mean?

thanks for your comments

bana can you define more what you are looking into??

My mom has Parkinson'd disease. When a person has been on the medication to control it for a long time, the meds eventually wear off quicker, causing the person to go into a trance like state. They may not be able to move or communicate until more of the meds are taken. On is when the med is working, and off is when it has worn off. That's the simple version. Google it and you will find many more explanations.