Blog: "Scuba diving in the sea makes my LongCOVID symptoms/PEM almost disappear. For the third time."

[Mij]

March 26, 2026

Dirk Paessler's Personal Blog

"I have long-term COVID. Not ME/CFS—I need to clarify that upfront because the distinction is important. My case is moderate: PEM, dysautonomia, and reduced stamina. I'm mostly functional, but always with a tight energy budget. People with severe ME/CFS live in a completely different energy frame—I don't presume to draw conclusions about their situation based on my experience.

But what happens to me when I dive is remarkable."

 

[Mij]

Reminded me of PG.

 

[Jonathan Edwards]

Note that when in the sea you are effectively weightless, as in space, so there is likely to be no OI.

 

[Jonathan Edwards]

Reminded me of PG.

He has been in outer space for some time.
On planet Zog, maybe, totally covered in warm salty water and mangrove piña colada forests.

 

[Mij]

He says he has "moderate PEM" and dysautonomia, but not ME. Ok.

I feel worse in a heated pool, whether I'm floating around or standing.

 

[SNT Gatchaman]

For the third time diving holiday with LongCOVID. For the third time the same thing: After the first dives, something changes. With each day it becomes clearer. After twelve days with daily 1-2 dives (Nitrox 32%, 20-30 meters deep, almost 1h per dive) I feel instantly healthy.

FWIW this paper notes "we observed a transient decrease in mRNA for HMGB1 and a decrease in mRNA for TLR4 immediately after the dive." Fold change for TLR4 —



The Impact of Recreational Diving to a Depth of 40 m on Selected Intracellular DAMPs (2025)

Spoiler: Abstract

Increasingly popular, recreational diving is a physical activity that takes place under extreme environmental conditions, which include hyperoxia, hyperbaria and exposure to cold water. The effects of these factors on the human body induce increased levels of reactive oxygen and nitrogen species in divers’ bodies, which may modulate damage-associated molecular pattern (DAMPs), their receptors and the antioxidant response.

This study involved 21 divers who descended to a depth of 40 metres. Determinations of selected intracellular DAMPs (high-mobility group box protein 1,HMGB1, S100 calcium-binding proteins A9 and A8, S100A8 and S100A9, heat shock protein family A member 1A, HSPA1A (Hsp70), heat shock protein family B, (small) member 1, HSPB1(Hsp27), thioredoxin, TXN), their receptors (Toll-like receptor 4, TLR4 and receptors for advanced glycation end products, RAGE), nuclear factor-κB (NF-κB) and antioxidant defence markers were performed before, after and 1 h after the dive.

A significant transient reduction in HMGB1 expression was observed immediately after the dive at both the mRNA and protein levels. We noted an increase in S100A9 expression, which occurred 1 h post-dive compared to the post-dive time point, and a post-dive decrease in TLR4 expression only at the mRNA level. Diving also influenced the expression of genes encoding key enzymes associated with glutathione synthesis, (glutamate-cysteine ligase, catalytic subunit, GCLC and glutathione synthetase, GSS), and reduced plasma glutathione levels. However, no significant changes were observed in the expression of NF-κB, nitric oxide synthase 2 (NOS2) or circulating DAMP receptors (TLR4 and RAGE).

The findings suggest an adaptive response to diving-induced oxidative stress, which appears to be a protective mechanism against an excessive inflammatory response. To our knowledge, this is the first study to analyse the role of intracellular DAMPs in recreational divers.

Web | PDF | International Journal of Molecular Sciences | Open Access

 

[Utsikt]

Note that when in the sea you are effectively weightless, as in space, so there is likely to be no OI.

I don’t understand. Wouldn’t your internal systems still experience the same pull of gravity in water? You’re just floating due to buoyancy. In space you’re in a free fall at a constant speed.

 

[Liie]

I don’t understand. Wouldn’t your internal systems still experience the same pull of gravity in water? You’re just floating due to buoyancy. In space you’re in a free fall at a constant speed.

I have an intuitive feeling that Jonathan is right, but I can't really figure out why... Interesting! I think maybe you can think about it like this:

When standing the body is like a narrow barrel of fluid. The pressure at the bottom of the barrel (corresponding to the feet) is at 2 meter depth, and the fluid pressure is that of 2 meters.

When submerged the water pressure outside the body counter-acts the internal pressure in the body.

So the water acts like a perfect full-body compression stocking.

The water pressure is not exactly the same as being weightless, but has some important similarities.

 

[Utsikt]

I have an intuitive feeling that Jonathan is right, but I can't really figure out why... Interesting! I think maybe you can think about it like this:

When standing the body is like a narrow barrel of fluid. The pressure at the bottom of the barrel (corresponding to the feet) is at 2 meter depth, and the fluid pressure is that of 2 meters.

When submerged the water pressure outside the body counter-acts the internal pressure in the body.

So the water acts like a perfect full-body compression stocking.

The water pressure is not exactly the same as being weightless, but has some important similarities.

Isn’t that effectively like what happens when lying down because the difference in pressure from top to bottom is just from 15-20 cm? Lying down presumably doesn’t produce the scuba effect, or else he would have told us.

And I assume you’re mostly horisontal when scuba diving. So something else must be going on. I think the compression stocking analogy might be onto something if it affects the peripheral blood supply in a different way than lying down does.

 

[Jonathan Edwards]

Isn’t that effectively like what happens when lying down because the difference in pressure from top to bottom is just from 15-20 cm? Lying down presumably doesn’t produce the scuba effect, or else he would have told us.

Even lying down is different because the underneath parts of you are under the downward pressure of the top parts. In water hat downward pressure is counteracted by pressure from surrounding water. You are weightless for all practical purposes. One of the few differences is that your bone-locked semicircular canals are not affected by the surrounding water so you can still have a sense of being the right way up.

 

[MrMagoo]

Ive recently located a warm swimming pool I’m going to try, I’m very much a water baby and never happier than in water.

I used to find that when I got out of a pool, the gravity really hits me like I’m made of lead. Not met anyone else who has that sensation. Always took me a while to adjust. Fine when in the sea though.
It’s exactly the same as when I’m struggling and crashing, gravity feels heavy. Will be interesting to see next month how I get on after my first dip since before covidtimes.

Would happily live in a warm water tank, 43C ideally, pm me if you want me to take part in an experiment.