I wonder, what if constant negative thinking, lots of negative feelings, and being stuck in the mind causes great fatigue?
According to tradition, every act of body, speech - and so also mind - does cause repercussions, but mostly in a rather distant future, when necessary co-conditions come to fruition too. Kamma, as it is called in Pali (= acts and effects).
The western concept of 'positive thinking' on the other hand differs, in that it proposes nearby fruition. Which on the opposite doesn't consider the possibility of the near present already predetermined by, in part, a very distant past.
Co-conditions already present, it does work very well for some. And therefore give them the premature impression, it might help everyone in the same immediate way, As proposed in some self-help books. But usually it doesn't, due to the lack of co-factors from the past.
Buddhist teaching is amongst many things understanding that everything changes and that staying calm until it does is beneficial.
There is however this immediate effect of wholesome ideation, that it does increase resilience in the face of overly challenging experiences. With rather instantaneous effects starting in the nervous system.
Since this thread is about our own stories, here is mine when starting vipassana meditation 30 years ago:
From overall strong and healthy (during a rucksack world travel), within month I suffered palmo-pustular psoriasis, where both my feet soles blistered and festered for in total 8 months. Placing me in the horizontal that long. Gladly in a spiritual place like Dharamshala, I got ayurvedic, homeopathic and Tibetan medicine support (even by Yeshi Dhonden, the former personal physician of the Dalai Lama). Which, just as a 10-day course of antibiotics, didn't bring lasting relieve.
I persisted with in total 1 and half year of whole-day vipassana practice retreats, which culminated about 4 years later in a further 8 months horizontal placement, now due to a very painful spondilodiscitis. Gladly again in a place as Bodhgaya, with much peer support too.
However, the above described immediate nervous system effect already with the first incidence in effect, cheering up my medical peer support was somehow perplexing to me, when they sometimes lost hope (not verbally, but in desperate facial expressions) with my intractable case. - 'This, too, will pass.'
He also talks about Presence and how to get more energy and be more alive when connecting to your inner presence.
So yes - and no. Increasing presence and energy can give you also the precondition of being able to better cope with terrible stuff from the past, which thereby seems to come up easier. At least in my case, with 2 bed-binding 8-months lasting diseases
I made even the funny experience of 2 distinct effects of the 2 distinct meditation methods taught in vipassana retreats, one-pointedness and mindfulness (samadha and satipatthana). During the incident in Dharamshala, festering decreased with the former, but always increased greatly with the latter.
there is something beyond our normal 'consciousness', our ego, our life story, something unborn and eternal. They call it 'annatta', or non-Self.
To nitpick

, since all our constituent parts (body, feeling, thought, intentions and consciousnesses) exist out of 'non-self' elements and co-factors, it is not 'beyond' at all. But right here in this body, thoughts, feelings, intention and consciousnesses. 'Anatta', by the way.
As one Buddhist monk once said: The essence of Buddhism is '
no self, no problems'.
I think this is very deep.
The most perplexing about 'non-self', I found, was not that selves always cease with inherent impermanence, But that one never even existed as one always thought, one would. With attachment to projections, this is a terrifying experience. The 'no problem' part only surfaces with mean challenges later.
I might have really failed.

Because with further chronic degenerative diseases starting only 16 years ago, I've got to know another part in me, unknown before, in that I fought for my health, as if my life depends on it (=attachment). With natural means and persistence I actually did experience remissions of PAD, COPD and post-exertional malaise.
However... attachment = non-self = no problem.
But none can it explain it better, than
https://www.accesstoinsight.org/tipitaka/kn/ud/ud.1.10.than.html
"Then, Bāhiya, you should train yourself thus: In reference to the seen, there will be only the seen. In reference to the heard, only the heard. In reference to the sensed, only the sensed. In reference to the cognized, only the cognized. That is how you should train yourself. When for you there will be only the seen in reference to the seen, only the heard in reference to the heard, only the sensed in reference to the sensed, only the cognized in reference to the cognized, then, Bāhiya, there is no you in connection with that. When there is no you in connection with that, there is no you there. When there is no you there, you are neither here nor yonder nor between the two. This, just this, is the end of stress."
Though
Bāhiya seems to have experienced similar complications after starting mindfulness practice, as me to a much lesser extent,
Now, not long after the Blessed One's departure, Bāhiya was attacked & killed by a cow with a young calf.
The big lesson learned and embodied: Never push self-help methods (or religion) on others in need, if they don't search it out themselves. Some may not be ready for also tire consequences, at times.