I find the explanation of trying to raise body temperature upon waking a
little hard to believe. Ours sleep together in a "ball" under an a lot of
blankets and if you pick one up as soon as it wakes it is _very_ warm. I had
suspected one of the following possibilities may be at work.
 
1. If I carry one of ours into a strange surrounding (e.g. outdoors in
bright sunlight) they start to shiver.  Hence I wonder if it might be a fear
or uncertainty driven reaction.  In the case of just waking this might be
because they are not yet fully "with it" and ready to react to their
surroundings.
 
2. I've noticed that if I'm handling one of ours and then it strats to
shiver that that is shortly followed by urination or a bowel movement. I
take this as a sign to put them in the box quickly! Maybe the waking
reaction is a preamble to the morning movement as that is usually the first
place they head for when they wake up.
[Posted in FML issue 1433]