I had an experience of oneness about five years ago. It lasted for about one full day.
Forget about experiences. Don't worry about it; you might have had it, so what? It has gone and what has gone is not real. What is real will never leave you and it has never left you, it is there even now.
We should not hanker for experiences. Experiences are also fleeting. They come and they go. Pleasant or unpleasant, good or bad, all experiences are fleeting, and the relative are always fleeting, they come and they go. You are not that!
Focus on the person who has the experience. Who is experiencing now? And who experienced it then? Who is that who wants an experience now? That person is there even now, right now, and that is real!
The person who is craving for the experience is more important than the experience. One day experience of yours is worth nothing. Good it went off in one day. That which is not true comes for one day and it leaves. That which is the truth, is inside you and stays forever; and that is the experiencer. Got it?