6. Alternating day and night

In order to establish a possible correlation between health status and activity expression, we have taken up a very simple phenomenon of alternating daytime and night-time activity levels , which can be stated as follows: daytime activity levels are lower after a bad night (restless sleep). Thus, we postulated that a low (high) level of activity during both day and night can be a warning signal. This principle was confirmed by geriatricians in two hospitals where we followed five elderly people over several months. Figure