One way to know you are experiencing the ego and not the Self is that the ego always experiences itself in comparison to others. The ego never feels fully equal to others: it sees others as higher or lower, as better or worse. The Self sees everything and everyone as equal to itself.
The ego bears the same relationship to the Self as does a light-bulb to the electrical current coursing through it. The bulb looks as if it gives light independently, but in fact it doesn't. It is just a container. The true source of illumination is the electrical current that runs through the bulb.
In the same way, it is Self that gives energy to the ego and enables the ego to perform its function of making you think that the boundaries it sets are the real you. The ego is a useful instrument. For one thing, if it weren't for the ego, we would have no feeling of being an individual self. The ego tells us who we are in the limited, worldly sense; where the body comes from, how old it is, what we 'like' and 'don't like'. So, the ego is not always a bad thing or an enemy to exiripate. It is simply limited - and limiting.
To become fully in the Self, we penetrate beyond the ego's confining messages. Once as you let go of identifying with the body, mind, and emotions, then you naturally experience yourself as vastness, as pure being, as joy, as Awareness, as light. The Self has three main qualities: (1) sat - permanently real, (2) chit - aware of itself and everything else, and (3) Ananda - joyful.
-the lovely Sally Kempton.