I take 8000 D3 (+200ug K2 MK7) daily and I'm fine. since covid I go like this for entirety of winter and then back down when summer comes. Perhaps you live in a climate where you get a lot of sun exposure and somehow overdosed on that. A guy from vitadmindwiki.com even says that you'd have to take 14000IU daily for a year until reaching toxicity limit (although this guy tends to sometimes say different things on the same topic, so I'd be cautious on whether this is the exact amount)
https://vitamindwiki.com/Overview+Toxicity+of+vitamin+D
Although it'd be great if you explained what exactly happened, perhaps it wasn't a result of taking vitamin D itself but rather some external thing. Judging by "painful experience" I assume kidney stones, which could be caused by too much calcium or genetic preference. not a doctor or an expert on the topic though, just open for a discussion :)
The symptoms are hard to describe (but did not include kidney stones), but it was obvious that something was drastically wrong and the drastic wrongness went away in response to my completely avoiding all sunlight and dietary sources of vitamin D and my doing a few other things described below.
Most people could probably take as much supplemental vitamin D as I did without incurring this adverse effect, but there is no straightforward way for a person to know whether they are in the minority of people who will incur the effect. (I do remember that having Northern European ancestry makes the effect more likely.)
The drastic wrongness started showing up after only a few months of whatever high dose of D I was taking (and I regret that I cannot provide this information: I did search for it briefly; but it was definitely not an "absurd amount") so if you've been taking the 8000 D3 for years, then the drastic wrongness is unlikely to suddenly show up in your case -- and if it does show up it would probably be because you contracted some sort of chronic infection.
The presence of certain kinds of chronic infections and genetics are the main causative factors according to the information I relied on 25 years ago. Actually, here is the basic information. I followed most aspects of the protocol including my obtaining a prescription for olmesartan, but then I lost interest when the drastic wrongness went away (after not much longer than 4 months IIRC). I was also probably on an antibiotic during this recovery.
P.S., I take as much MK7 as you do (i.e., twice as much as the "suggested usage" on the label) and have for many years, just without supplemental vitamin D.
Most interesting, will bear that in mind. To this date I haven't encountered any "drastically wrong" symptoms with my d3 usage and frankly haven't heard that much about any adverse events linked to vitamin d3. If you feel comfortable with that then you could disclose what exactly is that adverse effect you've been experiencing, but I see that you try to avoid this topic so no pressure :)
It's not that I'm unwilling to publish the information: it is just that I despair of putting into words how I knew something was drastically wrong with my physiology -- especially now that 25 years have gone by.
