Meditation practice is not relaxing at all. The effect after meditating might be in part feeling relaxed, but in general meditation is pretty hard work.
This is probably a very common misconception, you see all the pictures of people meditating at the beach in front of a beautiful sunset and think that meditating is like going to the spa, when in fact meditating is much more like the mental equivalent of going to the gym.
Also, in many occasions (especially during a 10 day retreat like Vipassana), it can be very uncomfortable if not outright physically painful (although usually never dangerous).
Especially the effect after it makes that work more fruitful, since for various hours I'll be less tense and more focused. For example, it'd make socializing more relaxing.
Those are 2 very valid reasons for me to call it relaxing. Then again, I find running and listening to certain music also relaxing. Because after a while, I get in an automated flow ("trance") akin to meditating.
The 3rd reason is that if I'm rather tired, mindfulness can potentially get me to sleep. I often (almost daily) do it before I go to sleep, and it aids me to get to sleep. I much prefer it over: overthinking, fantasizing, or masturbating/sex.
Its already painful for me to meditate whilst sitting instead of lying but one gets used to that. Its just untrained muscles getting trained. As long as you don't strain yourself, you're fine.
I've done all 3 of these (meditation as in mindfulness), and I disagree.
Of these 3, meditation is the most harmless. It is relaxing, not discomforting (I'll hook into this again at the end of my post).
Someone can start meditating or fasting without guidance (though I recommend guidance in both cases, especially concerning fasting) and resume normal life whenever they feel like it. With psychedelics, that one doesn't fly and if you do meditation in a group such as a 10 day Vipassana course or are in a religion or cult being forced to fast then you might also feel the same pressure. But that's an outlier; in general, meditation doesn't have such -or any- pressure. It is relaxing.
Finally, I've followed a mindfulness course for people with autism and there is no such thing as that with regards to psychedelics. The psychedelics also affected my autism, and in some situations made it much worse. All of that while I wasn't aware I had autism!