Surprising yourself is kind of funny. If you start thinking about what would be a good surprise, it’s not going to be a surprise by the time you do it.
There’s no requirement to make a life-altering maneuver (although you could.) All you have to do is suddenly and spontaneously do something other than the thing you were about to do. (Turn left, not procrastinate, stand on your head, write with the other hand, contact someone…) It could take a few minutes or it could take all day.
Afterwards, write a page about the experience and what it was like.
Give your work a title. Sign it and write the date on it, too.