At the age of Four, I was knocked out by a blow to the head with a baseball bat. Over the next 40 years I've been knocked out seven more times. In the last ten
Years I've noticed a real problem being able to function at a level that I think is normal, and have found in many ways that I behave in a way that I know can't be normal. A total lack of concentration, memory, and a constant run down feeling.
I was laid-off from my last job (with no chance of being called back) due to my slow performance, inattention to detail, poor attendance, and the inability to function in noisy situations. I could go on and on, but even this seems as pointless as anything else I do. Not to mention, this has taken me about an hour to write when it should have been a couple of minutes. Where do I turn? I'm broke, no job, no insurance, and no ambition. It's very scary. I used to be considered reliable and a person to turn to for answers. I used to make great money but now I couldn't care less. I'm afraid I'll end up homeless. My family wonders what's wrong with me. So do I. Where do go for help.

Yes, it's quite possible. Especially disturbance of the frontal lobe, which is actually divided into several regions with various functions ascribed to each. Apathy, fatigue, and inability to concentrate are well known traits that develop in some people. There are several neurological tests that can be given, as well as MRI or CT to identify physical changes, but there is no known treatment. You could qualify for disability (with a lot of work and good medical records). You are not alone - CEOs and professors end up working menial jobs and sitting around doing almost nothing. You might be able to find an online support group by researching 'frontal lobe syndrome.'

Some researchers suggest walking an hour each day, along a different route if possible each time, while listening to challenging audiobooks on an MP3 player and headphones, but that is so far just a suggestion. It is known that the brain does have some ability to use other areas to take over functions lost by injured areas.

(I do see in your other post that you did a lot of work removing a tree and it's stump to below ground level, a huge amount of work, and that takes something off the apathy part.)

To be tested, I'd suggest starting with the nearest university medical center.

Out of work, no money if in the US, talk to your welfare worker about medicaid.

See doctor if this is effecting job, about getting disability.

But yes, just one serious blow to the head can cause you to have no mental use at all.
I find it strange you were knocked out so many times, that is not common. Unless you were a pro boxer.

But look at many of the pro boxers, there decreased ability at times.