"The 3pm crash" is well documented and extremely common. Personally, I set up my schedule so I am not trying to do intellectual work between 3 and 4. Eat a snack, walk to the Starbucks down the street, go to the gym, take a boring meeting - anything, and then resume programming when my body is ready (usually around 4/4:30).
The Spanish have siestas.
There is nothing wrong with you - this is human nature. It's in the scientific literature, TV commercials for energy bars, and even some European cultural identities.
The Chinese also practice the afternoon nap. Lunch break at work in China is two hours: one for eating, one for sleeping. White-collar workers all get this long of a break. As for blue-collar, I don't know if factory workers do, but it certainly applies to shop owners, street vendors, and many moped/tricycle drivers.
Many people, especially shopkeepers and associates, sleep right at work! More than once I headed down to the cellphone store to recharge my minutes, only to remember the time when I found folks sleeping at the counter. Nothing for it but to return a little later.
Another popular way to sleep is to stretch out atop the seat and handlebars of one's e-bike (electric moped). Must be more comfortable than it looks.
The Spanish have siestas.
There is nothing wrong with you - this is human nature. It's in the scientific literature, TV commercials for energy bars, and even some European cultural identities.