I think freedom is a relative subject and is different for each individual and situation. Some might feel free when getting out from a bad relationship or job, while other will have this sentiment when escalating a mountain or drive a car on the highway. At our base, we feel free when we know we can do what we want at a certain moment, without bad repercussions. Even a slave can have his moments of freedom, even if from outside looks otherwise. To conclude, I think the feeling of freedom is not continuous (like the feeling of happiness for example), but as a consequence of some actions. Like everything in our lives, is a survival and evolution mechanism!