transmission problem

[guitar]

Ok, my transmission was doing the something that i didnt think was even possible. On my way back to school today i was driving on the free way all of a sudden my car takes it self out of overdrive and it wont engage back into it so i say whatever ill drive for a bit see what happens then a few miles later it started to switch in and out of overdrive on its own like every 5 seconds. So i stop for a bit trying to figure out what happens, i looked at it have no idea whats wrong so i decide to drive it again it wasnt taking itself in and out of overdrive on its own after that however everytime i tapped the brakes it would engage/disengage overdrive. i have no idea wtf would be wrong

 

[guitar]

anyone? im drove it for the first time again in a week, drove fine for like 20 minutes than started to do it again