BillyJoe said:
Superficially [difficult for the mind to imagine its own nonexistence], yes.
The implication of that statement seems to be that there's some
in-depth way to imagine one's own nonexistence. I don't believe that there is. Everything that you've ever experienced has been from within your consciousness as an existing being. (Before you existed you had no experience.) Even your imagining of what it's like to sleep comes from your experience.
How did you acquire an understanding of the word 'nonexistence' in the first place? Didn't it come from your having observed -- in your experience, personal and vicarious -- the disappearance of other creatures (which under certain circumstances you assume signals their nonexistence)? You've
experienced in your own existing mind the phenomena that you believe mean that they have ceased to exist (just as earlier you experienced the phenomena that made you think that they existed). Imagining their nonexistence is quite different from imagining that you yourself -- the imaginer -- has ceased to exist.
The very word 'imagine' implies existence on the part of the imaginer (though not necessarily on the part of the imagined). Trying to imagine your non-existence merely takes you further away from it. Paradoxically, if it could be imagined, it would be by ceasing to imagine at all. (Maybe you imagined it last night while you were asleep.

Even then, though, you'd be an existing being "not-imagining", so the experience of non-existence would be bogus. Any experience of non-existence (that is, experience of not having experience) would have to be illusory.
Speaking too implies existence on the part of the speaker, so speakers who speak about their imagining of nonexistence are compelled to speak nonsense. (Already -- just approaching the periphery -- I've been speaking mostly nonsense.) Try to avoid it if you wish, but I'll be very surprised if you succeed.