I am not sure this is related to psychology or not.
My friend casually commented to me that he feels his bag to be heavier after his meal. So I started observing my perception of weight of school bag after every meal. I did this for 3 weeks ( 1 log per day i.e. lunch, 5 days a week, 15 observations).
For 15 observations, 13 times I felt my bag to be heavier. These 13 times I had regular class after lunch. The other 2 times, I had an exam an hour later my lunch.
Is it psychological and / or body function related ?