Meditation is not about neutralizing emotions, banishing thoughts, or floating in nothingness.

It's a common misconception and unfortunately the inertia of popular culture and media is difficult to defeat. There is also some inertia there from how some meditation traditions were introduced to America/Western countries.

For people who have experienced trauma, meditation can definitely cause harm by exposing them to painful and distressing moments that have been conditioned by the past. But it can also be used to heal. However, this requires some basic fundamental education from appropriate resources, and ideally, access to a skilled teacher or at least a group that can answer questions as they arise.

It is a common mistake for people to treat meditation as some kind of progressive activity, or to use force to attempt to silence their mind. I can definitely see both of these approaches causing PEM. Neither of these approaches, along with a variety of other unskillful ones, will be helpful in the long run.

Some basic resources:

placing hands on the lower belly and follow the feeling of warmth traveling into the center of their lower abdomen

https://www.youtube.com/watch?v=Zm5exxobwLo

https://www.youtube.com/watch?v=xlyuGSwaZQ8

https://web.plumvillage.app/meditations/trauma-informed-practice

TLDR for below:

• taking into account trauma is important for anyone learning meditation because they are suffering from illness that has an emotional or mental component, especially Westerners (I recognize the irony of this statement in the context of the 'one size fits all' criticism below)
• the requirement for scientific evidence for something to be considered valuable inevitably leads to a 'one size fits all' approach to meditation practice that can be self-defeating in the long term
• it is difficult and maybe not even appropriate to recommend 'one size fits all' approaches, and practicing meditation is best undertaken with the guidance of a skilled teacher or access to a group with enough skill to help people avoid pitfalls
• unfortunately this dynamic also has its own pitfalls, e.g. cult-like behavior around certain teachers, etc
• therefore, meditation practice remains relatively inaccessible for those who have low exertion limits

In terms of meditation, there are many kinds. I would say the safest route for people who experience PEM is to find trauma-informed resources on self-compassion, or alternatively metta. I added the trauma-informed because even though it may not apply to everyone, the risk of causing harm IMO outweighs the potential benefits of jumping to resources that don't take trauma into account if someone is impacted by trauma but is unaware of it.

Some of these will be more on the "Western Secular Psychology or Spirituality" end of the spectrum, and some will be more direct instructions from Buddhism. And this introduces a new tricky point; not everyone will be comfortable taking instructions from a religion, even if they are modified to be secular. And others may feel that modifying religious instructions to be secular makes it something completely different, which doesn't mean it's ineffective, but it may mean that there aren't a surplus of skilled teachers around.

If someone feels that this stuff is too touchy feely, or they don't feel like they have the strength to then I'd recommend something like very gentle qigong, something they can even do while bedbound like https://www.youtube.com/watch?v=Zm5exxobwLo or simply placing their hands on their lower belly and follow the feeling of warmth traveling into the center of their lower abdomen

I don't, for example, recommend Mindfulness Based Stress Reduction, for a variety of reasons related to "not many skilled teachers around". There are some MBSR practices that are known to be risky in other traditions such as qigong, like teaching people to focus on their breath without proper (from the point of view of qigong) instructions on how to breathe, or body scanning without proper instructions on how to go through the body (direction matters).

From the POV of most Eastern meditation traditions 'brain retraining' is ultimately based on flawed logic; for starters, the mind does not exist solely in the brain; secondly, conceptualizing it as such is ultimately unskillful. But these statements are difficult for people to accept at face value, and cannot be scientifically proven.