How to organize time at the computer, so as not to "stupid" after a while?

Question

Work organization

Hi all!
Perhaps my problem will seem far-fetched, but it is. When I study programming for a long time at the computer, I notice that after 2-3 hours (sometimes after 40-50 minutes) I start to "stupid" - the information simply ceases to be assimilated, I read / watch and immediately forget everything.
Tell me, does anyone have the same problem?
How can it be solved?
I tried to alternate work at the computer and physical activity (I study programming for 2 hours, then I go to the garage for 2 hours to do some housework with my hands, then again at the computer for 2 hours, etc.), so the brain seems to have time to "load fuel "and mental clarity remains at a normal level, there is almost no" dullness ".
But this is non-systematic, I still forget to alternate, and I can’t immerse myself normally, I can’t concentrate if after exactly 2 hours I break away from the computer, and there is the middle of a video lesson or a chapter from a book.
Who faced similar - please, give advice how you overcame it and solved.
Thanks a lot!

Answer 1

after 2-3 hours (sometimes after 40-50 minutes) I start to "stupid"

this is a natural, absolutely normal state.
you are doing everything right.
you can try setting up a scheduler/alarm clock on your smartphone

Answer 2

In the first half of the day you work with clients on the phone and on the go, the second half at the computer and you won’t be stupid

Answer 3

The most valuable piece of advice I've gotten here is off-topic, but very similar and sometimes helps with dullness.
This is: sitting down at the computer, doing some task, not getting up until you do it.
(+ if you want to take a break, then take a break without leaving your computer, don’t lie down and don’t go to drink tea until the task is done, otherwise such an encouragement of weaving is obtained)
This may contradict advice on changing activities, but often you need to overcome your lack of involvement in the process and do at least some task, the logical part, without being distracted.
By myself, I noticed the following, which helps in learning - to delve into one topic and right during the day at any convenient moment, open a book, a lesson, write code on the topic being studied.
Video lessons are really different, for the last course I gave 14 thousand here, so after listening to the teacher’s boring voice, all the desire to study the topic disappeared.
Highlight tasks, do some kind of plan periodically, listen to yourself, each dullness is slightly different.
Upd:
+ For me, this is an ordinary wooden chair, do not fall apart, do not lean on the back, sit straight, but this is individual, it depends on health.
+ Communication with colleagues, like-minded people according to topic
+ Do not be shy to write down on paper, sometimes such stupidity rolls in that only paper saves.