Is there any reason of restlessness in the afternoon? I have been practicing mindfulness and watching thoughts.   I usually feel rapture, calm and desireless all the day but not in afternoon after lunch.  In afternoon, I even forget all stability including mindfulness &amp; various desires creeps in the mind. Situations become extraordinarily better after 4-4:30PM. 

Is there any particular reason of afternoon (2-4) instability? What can I do to let that not happen?
Restless drowsiness is common after eating. AN7.61 discusses remedies at length, including:


  But if by doing this you don’t shake off your drowsiness, then—percipient of what lies in front &amp; behind—set a distance to meditate walking back &amp; forth, your senses inwardly immersed, your mind not straying outwards. It’s possible that by doing this you will shake off your drowsiness.