One source of drowsy-at-work could be toxins.
I don’t have a lot of cause-and-effect here, but dealing with toxins was one of the things I did in my successful fight with drowsiness.
There are two separate issues here:
Keeping Toxins out of your System
Just think about it. All of those additives, preservatives, and medicines are going to have some residual effect. Enough said.
Dealing with the toxins already in your system
I had personally accumulated substantial anecdotal evidence that my own body was suffering under a load of mercury. This was partly due to an incident involving a broken mercury thermometer and partly due to amalgam dental fillings which seemed to set off a series of symptoms in me.
Anyway, I decided to have my mercury fillings replaced. (Most dentists are not set up to safely remove amalgam fillings. Do some research about mercury vapor toxicity and mercury-free dentistry if you’re serious about this undertaking.) This was done during the same time period during which I was taking the other actions recommended at right, so I can’t say for sure how pivotal this step was.
I did also research and use one heavy-metal-removal product.