Advice needed: collapsing from hard shots in rapier

I have a friend who has been struggling over the past few years with an issue and we haven't been able to figure out the cause of anything. I'm curious if anyone here has dealt with similar or has any advice.

The issue is that hard shots, for some reason, tend to trigger a reflex to collapse. They have been fencing for about 6 years total albeit sporadically at times due to real life commitments. At first we thought it was just a reaction to a hard shot to the head that had us performing a full concussion assessment (I was marshalling the bout, it was an excessive shot by far but thankfully no concussion). By the same person, there has been a hard shot to the liver that made them collapse as well which we chalked up to the pain causing that reaction. However, there have been situations since then of hard shots making them collapse, at least one came from me into their sternum (did not knock the wind out of them though it did bruise) and even shots to the face that while excessive, were not to the level of worries about concussion and would not have had the sharp pain of a hard shot to the body. They fence in a plastic chest protector now and I believe this has potentially helped some but it's unclear.

They have had this happen in one on one bouts as well as melees from shots to the head/mask, torso, gorget that have caused this reaction but we can't figure out why. They are not doing it intentionally at all and this is not something for sympathy or some ploy or anything. We're wondering if this could be a psychological reaction or potentially a medical one.

Has anyone had or seen similar occur or have any advice? "Toughen up" or "accept that it happens and deal with it" are not helpful, we are in a kingdom whose calibration standard is lightest touch. Any advice or questions are welcome. I will answer what I can and also am in touch with them and will provide any answers they are comfortable with. Thank you!

Edit to add: I agree that they should see a doctor and am checking with them if they have. If not, I know they are planning on it. We mainly wanted to check here to see if anyone had other thoughts. I think it is likely a trauma response because it doesn't seem to happen when hit in the arms or legs (that I know of). Thank you all for your thoughts

ADDITIONAL INFO: they have seen a physician and also had a CT scan done, everything came back normal, no issues