(setq scroll-margin 10)

(defun hang-callback ()
  (setq hang-sequence (random 4))
  (setq hang-lines (1+ (random 24)))
  (if (> hang-sequence 1)
      (message "sequence %d lines %d" hang-sequence hang-lines)
      (message "sequence %d" hang-sequence))
  (if (equal hang-sequence 0) (next-line))
  (if (equal hang-sequence 1) (previous-line))
  (if (equal hang-sequence 2) (scroll-down hang-lines))
  (if (equal hang-sequence 3) (scroll-up hang-lines)))

(defun hang-exec ()
  (interactive)
  (run-at-time nil 1 'hang-callback))