Over the last 6 years, the biggest obstacle I have found to doing consistent samadhi (meditation) practice is NOT physical pain, nor is it lack of concentration or lack of will (e.g. getting fidgety and wanting to get up and do something), but rather, it is a gross malaise that creeps in during my sitting. I'll mediate consistently for a week or so, but by the second week, every time I sit dow,n I get this heavy depressed feeling, and I start have hazy flashbacks to unpleasant or boring times in my life (it's rather banal, not like a Stephen King tremor or anything). The result is that I feel quite anxious and I have to get up and walk around to relax. It's not like my samadhi per se is poor- I'll be capable of counting all my breaths without interruption, it's just the background buzz in my brain is this nauseating malaise.

I know I'm supposed to "let it be" and not get involved with it, but what do you do when your mind is so out of control that's not even possible?

Over the last 6 years, the biggest obstacle I have found to doing consistent samadhi (meditation) practice is NOT physical pain, nor is it lack of concentration or lack of will (e.g. getting fidgety and wanting to get up and do something), but rather, it is a gross malaise that creeps in during my sitting. I'll mediate consistently for a week or so, but by the second week, every time I sit dow,n I get this heavy depressed feeling, and I start have hazy flashbacks to unpleasant or boring times in my life (it's rather banal, not like a Stephen King tremor or anything). The result is that I feel quite anxious and I have to get up and walk around to relax. It's not like my samadhi per se is poor- I'll be capable of counting all my breaths without interruption, it's just the background buzz in my brain is this nauseating malaise.

I know I'm supposed to "let it be" and not get involved with it, but what do you do when your mind is so out of control that's not even possible?

It's normal for meditators to experience what you've described to some extent, but it sounds like you are experiencing much more intensity.

What causes the hazy flashbacks to arise?

What causes the heavy depressed feeling to arise?

What causes the anxiety to arise?

What causes the nauseating malaise to arise?

You've got several sensations arising but have you noticed what order they arise in? Does one cause the other? Or do they arise according to other conditions that you haven't mentioned?

Next time you sit just watch and wait for these things to arise, see if you can detect a pattern?

Your question gives me the impression you are trying to do concentration practice, trying to focus on one object. I'd change tack as an experiment, focus you attention on the quality of awareness, let the awareness be as broad as possible, let everything in rather than choosing one object.

Here you've got a good learning opportunity.

This is probably where you have reached a certain obstacle to further progress....perhaps torpor....which can cause an unnatural sleepiness and lack of clarity. It has to be overcome by increased effort and vigor....perhaps shorter sessions...more walking...reduced diet or fasting.....but once broken through will lead to rapid advancement.

In Vipassana the teachers refer to this as an insight where one becomes bored with life and existence..... followed by desire for escape from rebirth...desire for release.

Do you have a meditation teacher? This is something that is ordinarily explored in personal discussions between meditator and instructor.

What system of 'samadhi' meditation are you practicing? It might be time to move on to satipatthana vipassana, if you're on a Theravada path.