I am seeing a therapist, and here are some more exercises he
suggests:

  - sit straight up as if your skull was suspended from a string.
    don't forcibly straighten your back though. make sure to sit
    exactly on the bones in your buttcheeks. concentrate on
    breathing.
  - tilt your upper body slightly to either side so that the arm
    dangles loosely. now shake the wrist a couple of times while
    keeping the shoulders loose.
  - stand up, let your arms swing sloppily to either side (left hand
    to right pocket in front of body, right hand to left pocket
    behind body, then vice versa). don't exercise force, just let
    them swing.
  - walk up to the door frame, get upper arm horizontal, point lower
    arm vertically upwards at 90 degrees. hold lower arm to door
    frame, turn upper body away to stretch the chest muscles
  - sit on ground, make soles of feet touch each other. fold hands
    behind neck, elbows between knees, gently pull down the neck and
    entire upper body. breathe normally!

maybe upstream could visualise these, i suck at drawing. and no,
please don't ask me to use bugzilla at workrave.org.

Here are two more:

  - standing up, let your arms dangle down both sides and swing them
    back and forth, but only slightly, maybe 20-30 degrees each way.
    concentrate on feeling the weight of your arms.

  - standing up, bend your knees a little, then extrude them; repeat
    in quick succession. feel your upper body shake and try to let
    your arms dangle, let them pick up on the swing.