Why do we get so tied after laying in the hot sun?

Question

I run and aerobics, so why am I so tied after laying in the sun for a couple of hours life I ran a marathon?

Answer 1

Perhaps your body is working overtime to keep you cool.  Any process your body performs comes at a cost of energy.  That energy in turn will require your body to need rest, and you will be able to sense that as being tired.  

On the same note, if you are in freezing temperatures your body will struggle to stay warm, spending massive amounts of energy.  You will eventually grow very weak.    

Not physically moving your body just means your voluntary muscles are not using energy.   The rest of your body is constantly using energy.  Even thinking hard for extended periods of time will drain your energy.

Additional:   it may also be that when laying out there for several hours you become totally relaxed and just naturally become tired.   The sun is quite refreshing and makes me feel at ease and peacful...makes me want to take a nap when i lie on the beach

Answer 2

Maybe it's heatstroke?

Answer 3

We are so used to driving our bodies with our will, to forcing our bodies to run and act, that we can easily be deeply exhausted and not really know it, When you lie in the sun, your body gets the signals to relax deeply and to rest deeply. The exhaustion you feel is likely a deep exhaustion from too much unrelenting activity, and the 'poor' body is reluctant to return to over-drive mode.