What could be the cause of near-feinting during a run when over 50?

Good day everyone! I am a new member of the forum. I was looking for advice if anyone else has had feinting or near-feinting spells during running, even though you feel amazing.
I am a man of 57, I usually run 3-4 times a week on a treadmill when the weather is not nice. Occasionally and semi-frequently, I am running along, and feeling fantastic, when all of a sudden a tsunami sized wave of dizziness that makes me want to feint immediately. Most of the time I collapse, or sometimes I can just place my feet off the treadmill and hold on until the discombobulation goes away. Usually about 30 seconds. I don’t understand it because I feel so great before it comes on. I went to a cardiac specialist doctor, angiogram came out great, they strapped me with sensors to monitor my heart activity during a normal day and he saw no problems. I’m 6 foot and 165 pounds and in good shape, otherwise.

Has anyone had similar experiences?

I haven’t experienced this
I’m sorry to hear you are experiencing this. It sounds very unpleasant, and worrying .
You don’t mention whether your running is really hard , where you get completely out of breath, or whether you are doing easier pace where you are not out of breath, zone 1 or 2.
Did the cardiologist test you on a running machine, or excersise bike ,and ask you to simulate the activity you do when these episodes happen? And to push yourself hard?
On your “normal” day did you do your run when you were wired up to the sensors?
I think if you provide some more information , like how long you’ve been training ,(years) , whether this is a new problem ,etc etc. Someone on here might be able to help you .
Did he/she give you any advice as to where to go next, seeing as they seemed to have ruled out it being a cardiac problem?

Is this only happening on the treadmill or does it occur during outdoor runs as well? I find that on treadmills I have to be cautious about maintaining my focus and only looking straight ahead, or I will suddenly become very disoriented and dizzy. I have no problems when jogging outside. I believe it has something to do with the brain receiving mixed signals from the eyes vs. the inner ear (?).

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Did you wear the holter monitor while on your treadmill and during an episode when you experienced the dizziness? That would give a good indicator if you were experiencing a rhythm issue that was causing your near-feinting. That would be my suggestion.

Are you watching videos on the treadmill while running? You could be experiencing vertigo front the moving screen but you and your surroundings aren’t moving. Kinda like getting carsick.

Does it happen when you slow or pause?
If so this can be caused by a sudden drop in blood pressure
Or it can be caused by a general low blood pressure

Thank you for your responses. So, firstly, yes, i wore the holster monitor while running on the treadmill in the doctors office(called a stress test) and no incidents happened, mind you they never happened every time i run, sometimes once a week, sometimes twice. I don’t stare at the TV, while running, it kinda bores me,my mind just wanders around the room, and mostly i’'m listening to my music on my ear buds.
Secondly, since i’m on a treadmill the pace is set and consistent. Usually 10km/hour, for 30 minutes and that is consistent. Strangely, i am never out of breath, i always feel like i’m on top of the world and could run forever. I’ve "gaps"in my routine, but lately i’ve been consistent, the last year. When younger, i would always run 8km about 3 times a week. I’m only running indoors on a treadmill because i live in a hot climate country. These incidences only happen when i’m on my constant tread mill pace.
Though…you did make me wonder about one thing. I do feel…kinda…sometimes…like a little dizzy when my focus is somewhere else,and i need to make a concerted effort to change my focus onto something else to make the (maybe) dizziness go away.
Someone, not a serious runner, opined that maybe, i’m not hydrated enough, or i should try eating something right before a run.
The cardiac specialist, had no more medical advice to offer, since he never got back to me, after i sent him blood pressure readings, immediately after a "near-feinting"spell.

Does it kinda feel like when you stand up from the couch too fast and your vision blurs and your feel dizzy or light headed? Cause it sounds like an episode of Vasovagal Syncope (aka Orthostatic Hypotension). It can be brought on by a myriad of things. But depending on how close you are to the wall in front of you it sounds like it could be a bit of vertigo and then maybe exacerbated by dehydration.

I’ve had that dizziness, fuzzy, tunnel feeling before when focusing on something too close to me and, like you said, it can help to look somewhere else. I never get it while working out but I imagine it could if brought on by other factors.

Well,this isn’t just a little bit of dizziness or light headedness, this is more like a tidal wave of dizzinesss that knocks me on my ass, literally, and i feel complete discombobulation for about 30 seconds before i come around.
On a possible similar note/feeling,when i am bench pressing a heavy weight, right after , i sit up and feel a dizzy spell coming on, but it doesn’t knock me on my ass, because, by stopping, and then sitting up on the bench, i’m already removing the stress and coming around, but i almost feel like, if the heavy lifting had continued, the dizzy spell might exacerbate, but like i said, it kinda felt like that. I’m starting to lean towards insufficient hydration before running.

I doubt if it is related to hydration, but I guess you have to start by eliminating the possible causes one by one.
It sounds a bit like vertigo to me, but I’m only guessing , and am not qualified to give you advice.
It sounds as though you are not overdoing it on your runs, and not getting out of breath. I feel a bit dizzy after doing Spanish Needle ,but I’m right at my limits there.
Keep us posted with how you get on, hope you get it sorted