I exist – I am sure of that. After all, some say that ones existence may only be an illusion – but how can something nonexistent experience an illusion?
For example, an illusion is defined as ‘a thing that is or is likely to be wrongly perceived or interpreted by the senses’. If I don’t exist – how could I possibly experience an ‘illusion’? Some part of me must ‘exist’ in order to perceive an illusion.
A second definition of an illusion is ‘a false idea or belief’. Similar to the first definition, in order to have or hold some belief (whether true or false) one must exist to hold that belief. I must exist to have a belief. If my existence is an illusion, that would mean that I am nonexistent – hence I wouldn’t be able to believe or perceive anything – indeed ‘I’ wouldn’t be anything – because I wouldn’t exist.
To say that my existence, my pure existence in the most bare sense of the word, is an illusion would be wrong. But there is the possibility that parts of my existence are an illusion. Not the whole of my existence itself – but parts of it.
I exist but I may perceive my existence in a different light than it truly is. For example, the Hindu teacher Shankara taught that everything is one, and that the ‘differences’ or ‘contradictions’ we see are merely illusions. In other words, this means that I exist, but that my own personal identity, my sense of being an individual, my unqiue psyche – all of this is an illusion. I and everyone else are all the same – we are all the same existence. Illusion is what causes us to see or perceive a ‘self’ that is separate from other ‘selves’.
So, technically my own view of my existence may be an illusion, but the actual existence itself is not an illusion. One must exist in order to question ones own existence. Something has to exist in order to experience an illusion. So, the act of wondering if you really exist or not is rather pointless. (Although, one could argue that there is no ‘you’ – that we’re all one and therefore an idea of ‘you’ is an illusion, but nonetheless even if everything is ‘one’ there is still some kind of existence in place)
Tl;dr there is some sort of existence that constitutes ‘you’, however the experience or feeling of an ‘individual you’, that is, a ‘you’ separate from others, may be an illusion.