Also, what was your reasoning for doubting that you exist? How was Descartes proof insufficient?

It's essentially circular. It assumes an "I" from the start. If you get rid of that assumption, you have to start with "something is thinking."

That's been acknowledged in philosophical circles for some time now, but I don't think many philosophers regard it as an important problem anymore. It's about as safe an assumption as you can possibly make.

If anyone wants to google this, keywords are "nonduality" and "Advaita". It probably deserves a memetic hazard warning, though.

Kary Mullis invented PCR while on LSD

I've heard more people than I care to recall claim inspiration from altered states of consciousness, but it would be a first to have anyone present one that's novel and demonstrably true.

Well, I've written a few poems and passages of longer prose that came out reasonably well and have joined the collection of "things I'm working on to submit to publishers" while on various drugs. That might just about count.

Also, is fun itself not enough to justify something being a Good Thing?

Let the people suppose that knowledge means knowing things entirely; the philosopher must say to himself: When I analyze the process that is expressed in the sentence, "I think," I find a whole series of daring assertions that would be difficult, perhaps impossible, to prove; for example that it is I who think, that there must necessarily be something that thinks, that thinking is an activity and operation on the part of a being who is thought of as a cause, that there is an "ego," and, finally, that it is already determined what is to be designated by thinking--that I know what thinking is. For if I had not already decided within myself what it is, by what standard could I determine whether that which is just happening is not perhaps "willing" or "feeling"?

Nietzsche, Beyond Good and Evil, aphorism 16

The message here doesn't seem truly novel, but 'You will survive through sex reassignment surgery' must at least count as unusual.

The story also illustrates how the word "I" can conceal any number of unsafe assumptions. Clearly part of the author knew more than she thought she did. (And the part about her childhood memories seems credible though not strictly proven.)

"something is thinking."

I thought the standard answer to this problem was that "think" confers "me-ness" - if you could observe "someone thinks" the way that Descartes observed it (introspection on the thought process) then you are that someone.

The flipside is that you can't know that others are thinking, because you have no ability to introspect on their thoughts.