Most of what the parasympathetic system does is regulate stuff like digestion and release of body wastes. You need some degree of peristalsis and bladder-fullness urge. Some OTC drugs will slow some of these -- e.g. Immodium -- but there are obvious unpleasant consequences if used for more than a day or two.
Maybe you can be quiescent for a few hours before bedtime, so most parasympathetic activities will be under way before you go to bed (i.e., do NOT work in flight-o-fight mode right up till bedtime). One cultural aspect of Spain, that is sure to keep the parasympathetic system well under way: the tendency to eat late at night.
I'm still really unsure what you mean, and as we say often on SP: you really should be talking to your doctor about this.
Perhaps s/he can prescribe a simple relaxant, or something like Lunesta, to make sleep easier and less disturbed.
Can you do any stretching? I certainly wouldn't want someone with a cervical injury to stretch the neck. But gradual stretching of the large muscles (e.g. the legs: http://www.abc-of-yoga.com/yogapractice/legpulls.asp
) releases endorphins to relax the body.