Help topic - mental stamina

Hello lichess community, I'm looking for your help.

The overall question is something like:

What do you do to improve your mental stamina for chess?

I'm a fairly underwhelming club player (ECF140 for those of you that means anything to) and I play league matches in the evenings as well as playing games for the county and the odd tournament. I often find myself getting extremely tired at some point during the average club game, sometimes with some quite embarrassing results, so I wanted to ask the above question (with a focus especially on getting insight from prodigious or prolific club/tournament players).

Are there any ways you can actually train your mental stamina? Are there any things that you as a player do before/during every game? Are there any ways you can give particular energy to that critical point in a match? Do you therefore conserve your energy in other ways?

So I'm expecting some fairly obvious (but probably good) answers like get good sleep or eat a banana during the game or whatever, but I also wondered whether anyone had anything that works for them that they'd be willing to share.

Best
Caustic

Define 'mental stamina'.

just do not play openings that requires a lot of thinking i assume would make it taking longer to become tired.

Daily meditation.

I usually avoid thinking when it's not my turn. That makes me get into time trouble sometimes but I'd rather relax while my opponent is thinking.

for me, i train my mental stamina by playing a lot of games, and it helps .It shows it's value when i play classical, i can calculate deeper and i don't drift away that much as i used to. So, the other advice would be to solve problems and puzzles without moving the pieces... i have a ches problem book in my club and i solved 1096 mate in two problems.so i "graduated" chess problemsso to speak. it is tough to build this kind of stamina but it never really goes away once you get to that point where 2 hrs of chess is nothing to you

I think sleep, exercising and some kind of meditation as suggested above are what help the most.

I am learning to be less emotional while playing. Stress and excitement burns up a lot of energy leaving the player burnt out.

You may have some clinical problem such as day-time somnolence (drowsiness) which is in the same family as narcolepsy. It's a clinical condition that can be diagnosed with a sleep study. It is often treated with dexamphetamines but there are other strategies such as exercise and moderate doses of caffeine in the morning and afternoon. Another cause can be sleep deprivation. Do you get adequate sleep and excercise? Another is postprandial drowsiness which is a normal response after a heavy meal but in some cases can be related to an abnormal rise in blood sugar levels immediately after meals due to hormonal responses not related to diabetes. Diabetes can be at a sub-acute level that may not show up with fasting blood sugar levels and will need a glucose tolerance test. Visit your doctor to get a professional opinion if required but it may be a simple explanation such as over work, fatigue from study or excess stress.
People often play chess at a time when they are not at peak mental capacity which is usually somewhere between 10 am and 2 pm. This may be interesting for chess players: http://newstartclub.com/resources/detail/tips-for-achieving-peak-mental-performance

It depends what you mean by "I often find myself getting extremely tired at some point during the average club game, sometimes with some quite embarrassing results"

Do you mean embarrassing results like making a terrible blunder? Or do you mean you are falling asleep in your chair?

If it's the former then I'm sure people here have some good tips.
If it's the latter you might be better off seeking help from a medical professional rather than here.

Either way, you might get more targeted advice if we know more details of what the problem is.