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 :)
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.
https://mpkb.org/home/patients/protocol_overview
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.
Unless you eat the pills like candy, you're safe.