I got my hands on a SHEWM and the errors you describe explain a lot, @Hector Penman
. I used the device to find a restroom (finally!) and on my return to class found someone sitting in my seat--and it was ME!
Had I known about the dimensional skipping issues, the dimensional skipping issues, I may have taken greater care, but apparently concerns about the universe exploding if you meet your double are completely unfounded! My double and I get along great, and there were hugs and high-fives right off the bat, so I can say for the record that physical contact with your next-door reality double poses no threat whatsoever.
We've had a grand time playing no end of practical jokes on friends and taking turns shouldering the burdens of school work while the other sleeps in or goes on a lark. I only wonder if my credits are transferable back to your reality as I'd hate to make a mess of things back there.