Hi, 
I am looking for advice to regain concentration. 
Bakground: 
Started meditating April -20. Been meditating ~25 days per month. Total practice time 187 hours. 418 seasons.
Technique: 
TMI - was meditating at stage 6 in Januar -21. Reached atleast first pleasure jhana. Sometimes do warmup with metta. 
Problem: 
Have been stressed with work (normal stress) in April-June so concentration started to fade until I was at stage 1 again. Consequently motivation and session length were redcued. I now have vacation and are not seeing any progress when doing TMI. Very monkey mind, and when trying to focus on the nosetrils the mind wanders quickly. Have been wondering if could be a nutritional defiencay, since I started eating vegan two years ago. Any tips on lifestyle factors / meditation preparation / technique or general tips to get back on track? Should I try another style of meditation since I am not getting any progress and loses it all when stressful situations occur (will probably be unavoidble in my carrer)? 

Thanks, and happy holidays.

What about discussing it with your doctor? It could be a medical problem. 

In the meantime, I suggest practicing the brahmaviharas.

Thanks for the answer. Yes I am definitely going to talk to my doctor. Thanks, the brahmaviharas will probably be helpful. I have only heard of metta practice. But seems like there are three parts more to look into. 

Have you experienced this kind of progress loss? If so, what got you back on track?

Copy pasting from a comment of mine from another platform.

Quote

A while back I experienced a spectacular collapse of shamatha and ekagrata. I learnt some things from it, sharing it with you in case any of it applies. I am writing this comment as if I were speaking to myself, and actually for my own benefit, no intention of preaching .

1. Shamatha and ekagrata are results, they are not the practice
2. Shamatha and ekagrata are extremely fragile. They collapse all the time! At lower stages in TMI the collapse doesn't hurt, often isn't even noticed. A small hut has collapsed, who gives a shit!
3. At higher stages there is a greater degree of investment and also a heightened ability to notice collapses. A skyscraper has collapsed! It fucking hurts!
4. The knowledge of how to develop shamatha from scratch is not fragile! No matter where you are in terms of stages, you most probably got there through hard work, dedication and lots of repetition of techniques. The techniques are like grooves cut on your brain
5. All that is needed to recover from a collapse of shamatha again is complete acceptance that shamatha is a result, it doesn't belong to you, it is not a property or a defining quality of you. You know the techniques, you remember them distinctly and clearly in 'muscle memory' and not simply in terms of language and concepts - which is a good thing, set aside the sense of ownership of the result and just simply apply the technique
6. No matter what stage the collapse has happened, no matter what the reason may be (often there is no reason!), the thing that prevents the recovery of shamatha is a ferocity associated with the sense 'I am doing this'. Unfortunately there is no permanent solution to this sense. This sense is one of the core functions of the mind. The attribution of action to a placeholder, a fictitious/fabricated agent who possesses agency. So there is agency! but its attribution to the agent is problematic in general and certainly in the development of shamatha. Every time you feel resistance in the mind, find the concomitant sense of 'I don't like this', 'I am facing difficulty', 'I am restless', 'I am a stage 9 meditator, and look at what the fuck is happening' .... find this sense, let go of the breath and using slow deep abdominal breaths just relax into this sense, don't argue with it, don't suppress it, you can't. Just relax it, put it down, stop powering it. This act creates a brief separation due to which the mind realizes the gymnastics that it indulges in and actually does put down that sense of 'I'. Then go back to the breath and become a stage 1 meditator again and simply start applying the techniques. You will find that in a couple of days, a couple of sessions, maybe just a couple of breaths ..... you are back in stage 9!

​​​​​​​End Quote

Well,  I agree with Adi on most points, although it can at times seem a little more problematic than a skyscraper collapsing. Or maybe my heart is not developed enough to empathize with that type of situation. In any case, I lose my concentration on almost a daily basis, but it always comes back.

I mention a doctor because they are often well-equiped to shine a light on various parts of the mind, although they may or may not know this.

It's all good brother, rally all forces, get nutrition and sleep right, rebuild it shouldn't be too hard to get back to where you were. Mind remembers. 

Thanks, needed this. 

Thanks, back to the cushion then ;-)

Try relaxation exercises. The main cause of mental turbulence is stress and mental fatigue.
​​​​​​​
http://ncu9nc.blogspot.com/2020/08/preparing-for-meditation-with.html
Maybe you should try eating a little meat to see if it helps?