Is this how Betta fish dies??

[NYCorchidman]

I have had a blue/red colored betta fish since summer of 2012. He was already an adult when first bought although the body size did increase under my care.

Starting about May this year, he started to spend a lot of time lying on his side at the bottom of the tank.

At first I thought he was dead, but when I gently hit the tank, he would move around and only to return to that position.

In July, he did not eat anything at all.

Now he is eating, but he barely moves if at all.
Even when I try and startle him by hitting the tank, he will move in place for a second then back to lying down.

I read somewhere that Betta fish lives only for about couple of years, and if that is true, my fish must be just tired from being too old??

I do not see any strange physical signs of disease on his body at all. No fungus on the mouth, eyes, fins, and his scales are all even and smooth.

He looks perfectly fine except he just likes to play dead all the time now.

So, I'm wondering if this is how Betta fish naturally behave when too old.

Also, any suggestions as to what to do at this point.
I mean, he stays lying down the whole time pretty much and looking at him kind of makes me feel down.