[smart (OP)]

According to a recent research paper, sleeping reduces our metabolic rate by 15%. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2929498/

So, is taking a nap in the afternoon likely to influence metabolic homeostasis ?

[evan_au]

According to old research, running a marathon increases our metabolism by more than 15%.

For historical reasons, energy consumption for warm-blooded animals has been recorded as the Basal Metabolic Rate, which is defined as being at rest, awake, and not actively digesting any food.

It makes sense that energy consumption could be slightly lower when you are asleep, and sleep paralysis further reduces unconscious muscle movement compared to being awake and still.
See: https://en.wikipedia.org/wiki/Basal_metabolic_rate