This is pretty advanced and only best to try if you have an established meditation practice, are familiar with ego death or have experienced it before. If you are stuck in the emptiness practice, this is also a good next step.
It is what it says on the tin. As we meditate, we learn to watch the river of thoughts. In the “watch the watcher” practice we take it up a notch and attempt to see who is watching. It is explained very well below:
Surprise! Nobody is home. Seeing in practice that you are nothing, emptiness, the watching, the happening is terrifying and exhilarating at the same time. Now instead of trying to overcome emptiness, to go through it, I learn to accept it – I am dancing emptiness after all…
Nomad of the Universe 
I have certainly had ego death. I positively enjoy it. And yet when I consciously contemplate the fact that I probably do not exist the concept becomes quite alarming. But that contemplation of course comes at time when the ego is control.
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How interesting, Anthony! If you don’t mind, can you share what was your ego death experience? Or please share the blog post link if you wrote about it before.
It is a paradox – we don’t exist but we also do. Emptiness is not empty. So it is terrifying but also exhilarating. Go figure.
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It was an absorption in the whole and hence as an individual self I did not seem to exist. I was not entirely sure what the whole was but to be a part of it seemed infinitely better than being outside as a self. I always return from such an experience feeling that life is better.
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