How can we be sure this is reality?

[Confused Ape]

Zhuangzi. an influential Chinese philosopher who lived around the 4th century BCE wondered about the same kind of things.

Zuangzi Quotes

Once upon a time, I, Chuang Chou, dreamt I was a butterfly, fluttering hither and thither, to all intents and purposes a butterfly. I was conscious only of my happiness as a butterfly, unaware that I was Chou. Soon I awaked, and there I was, veritably myself again. Now I do not know whether I was then a man dreaming I was a butterfly, or whether I am now a butterfly, dreaming I am a man. Between a man and a butterfly there is necessarily a distinction. The transition is called the transformation of material things.

During our dreams we do not know we are dreaming. We may even dream of interpreting a dream. Only on waking do we know it was a dream. Only after the great awakening will we realize that this is the great dream. And yet fools think they are awake, presuming to know that they are rulers or herdsmen. How dense! You and Confucius are both dreaming, and I who say you are a dream am also a dream. Such is my tale. It will probably be called preposterous, but after ten thousand generations there may be a great sage who will be able to explain it, a trivial interval equivalent to the passage from morning to night.

I think we're still waiting for that great sage who will be able to explain it.