It seems like if you're so tired while you're at work that you actually want to take a nap, then maybe there is another underlying problem.
The biology term is 'arousal' and there are peaks in the morning and late afternoon, but around 1pm-ish your body naturally slows down and wants sleep. The effect is much stronger in children, but it's there with adults.
You don't feel like you could fall asleep because you've trained yourself not to, and you're most likely taking wakefulness promoting drugs all day.
There is: tiredness. Often, but not always, due to lack of sleep. A nap is the solution.
If you need 8 glasses of water a day to be at peak-performance but for whatever reason only manage to drink 7 in the morning, why not have that final glass sometime during the day? Same with sleep.
In fact it's absurd to think everybody can store energy upfront and power through 9 hours of activity without falling off towards the end.
Naps are natural.
Consider my opinion changed.
I suggest you recalibrate your definition of "normal".
I don't really fall asleep, but I found that just closing my eyes for this short amount of time gives me a tremendous boost of relaxation, especially when my mind gets into a dreamy state for a minute or so.
The amount of sleep a person needs and how long you can go without involuntarily fallin asleep seems to vary wildly though; a friend who I have reason to believe talks about working continiously for 3 days to catch a deadline. (The explanation was along the lines of: it hurts but what to do?) An ex colleague was also known to work through the night between working days.
Creative problem solving mindset needs room for thoughts to wander, and is incompatible with hurry.
I don't think that making any type of generalisations (eg. "people shouldn't be that tired") makes much sense.
The problem is that sometimes I am in the zone from like 10pm - 1am.
So naturally I am tired during the day. A few minutes to nap for 3 hours of "in the zone" ain't a bad trade off for a company in my opinion.