I remember one time I was going through the whole "magic pill makes you opposite sex/gender for a day" thing in my head, and as a cis dude, was pretty neutral/comfortable with the prospect until I gave myself a brief, very vivid hallucination of gender dysphoria at the thought of having to present in public as a woman.

First two thoughts in my head afterward: "Oh, so that's what gender dysphoria is", and "well that answers the question of 'how do I know I'm cis tho' pretty definitively", lmao