It is more complex than that. Drowsiness is most often caused by a sleep debt which is commonly accumulated over a period of insufficient sleeping. Renowned s

It is more complex than that. Drowsiness is most often caused by a sleep debt which is commonly accumulated over a period of insufficient sleeping. Renowned sleep researcher William Dement did a big study on this which figured prominently in a modern analysis of the subject here: https://www.ncbi.nlm.nih.gov/labs/pmc/articles/PMC2391074/ https://www.ncbi.nlm.nih.gov/labs/pmc/articles/PMC2391074/ This study does not focus on drowsiness specifically, but rather measuring the amount of daytime sleeping and looking for increases. Under most circumstances daytime naps are short whether driven by drowsiness or the cultural standard of siestas.