(Note: this isn't about disproving external world skepticism, but that past experiences actually happened and are not merely false memories.)
In short, I am asking you to imagine having a memory of your younger self and that younger self becomes conscious throughout the duration of the memory that you experience. Since that memory is a part of you surely the younger you is also you. Furthermore, since the younger self has just as much right to claim its experiences are real, does that not mean that your memories of the past are just as real as experiences your present self is having?
Descartes' "I think, therefore I am" should remove any doubt that I do not exist. At the very least Descartes' argument proves that experiences exist (though perhaps not the "I"). Although we doubt the existence of "I", we cannot doubt the existence of experiences. Sense-datum seems to be the bedrock of all knowledge. Even if we doubt whether past experiences really happened - we might think of these past experiences as fabricated memories - we still cannot doubt that they exist in present mind of the thinker (albeit as memories).
Since we can doubt whether experiences actually happened because they are events from the past, we seem to place extraordinary emphasis on the nature of the present moment in our account for what counts as direct conscious experience. So it is precisely that direct conscious experience that allows us to make the claim, "experiences exist".
Perhaps you want to say whenever you have a memory of your younger self your younger self (in the memory) is momentarily endowed with conscious experience for the duration that the memory lasts. Now, your younger self is consciously aware only of the time that he or she is in.
(Even though both your current self and the memory of your younger self are living in different times, the matter of whether a person is or is not in the present time does not impede on consciousness. For your current self could be living in the past. Rather, it is the direct nature of experiences, this persistent illusion of being in the present that allows for consciousness.)
Although your younger self is now conscious and is having exactly the same experiences that you remember your younger self to be having, and at the same time that you are remembering it, is it not the case that you can at that moment claim legitimately that past experiences actually happened? For they are happening simultaneously and are both equally real in the sense that both your present and younger self are experiencing direct conscious experiences.
I am curious to see how people will argue against this point (while allowing the hypothetical scenario).