Today I've done a 4 hours long uninterrupted mindfulness practice using TMI methods in preparation for long SDS sits and retreats. I've also recently watched a documentary about solitary confinement so I wanted to lock myself in a room for 4 hours and see how much suffering would arise sitting alone. This was only an introduction to more intense and deeper practice sessions.  The challenge was also meditating while lying down, cross-legged and walking around the room. I could maintain mindfulness relatively well if my body is absolutely still. SDS sits are still hard but my body got used to them. Things gets problematic when I start to move around. So I was rotating between these 3 postures every time I've experienced a challenge unique to that posture. For instance, Whenever I tensed up and experienced challenging emotions, I've layed down, relaxed and continued meditating.  Whenever laying down made me sleepy, I've started my brief walking meditation. (10-15 mins)   Whenever walking meditation disabled my introspective awareness, I've gone back to sitting posture. I can do 2 hours long SDS sits but I've never maintained 'high' degree of no-mind, stable attention and most importantly extrospective and introspective awareness uninterrupted for 4 hours.  I can tell that this is challenging but at the end of the 4 hours, I could have meditated for another hour. I've already passed the 'hellish' boredom and impatience phase in my nervous system. But this is mostly because this was not a strict SDS sit. I've allowed for movement between those 3 postures whenever I felt like giving up. The biggest challenge I've added was to meditate in a hot environment. Since I do breath practice with TMI, the air temperature matters. If the air is hot, it requires more skill to follow the breath sensations. Especially the out-breath.  Fortunately, I've realized that breath clarity is relative and expecting the breath to be super clear and vivid in hot environments is a mistake. It will be more subtle than usual but you should still keep in contact with it.  After the stabilization, I've immediately expanded my extrospective awareness to external sounds (traffic cars, street noise etc.) I've been practicing this for a while. So whenever I do that, I get into a state of no-mind if I can combine the breath stabilization with sound awareness at the same time. Since the breath is very subtle, I did find it challenging but after a while awareness just rested at sounds and my mind was free from thoughts for a long period of time. Just to clarify, this is a relative state of no-mind. I'm not experiencing profound states of 'cessation' and whatnot. There were still thoughts I am not aware of below the threshold of awareness. Throughout those 4 hours, I've experienced a VERY salient psychedelic experience for a few seconds which is common on LSD. I think this was 3 hours in. My bed has black dots with its design. These black dots have started to flash back and forth (as it occurs with colors on LSD). This was very noticeable and not subtle. In fact, if someone experienced those few seconds without the context, they would probably think I've taken LSD. The whole experience must have taken somewhere around 15 seconds.  After the flashy black dots, I've seen other more subtle patterns. These were not too intense or were not close to psychedelic visuals. I've maintained the technique and equanimity as these were occurring.  Sleepiness and dullness was a BIG challenge since I was not particularly alert starting this long session. I wanted to meditate while I was sluggish and not particularly concentrated. This made things 10 times harder. Thanks to walking meditation, I've managed to stay alert and aware. These 3 postures allowed me to cancel out each postures negative effects. That was an amazing experiment.  If I had more skill to maintain this degree of mindfulness for 20 more hours, I could have started to get some sense into how advanced yogis survive 10 years of solitary confinement. In my mind, everything has to do with acing spirituality for one day. I'm not talking about surviving a 18-24 hour uninterrupted mindfulness session. But to thrive doing so. To get through it with minimal suffering. Only then can you take on longer retreats and solitary confinement like circumstances with skill and confidence. If you can do 1 day, you can also do consecutive days. That will take some skill as well but the issue is that an average meditator can't even manage a full day of hardcore spirituality without getting hellishly bored or experiencing the meditation as torture. I'm currently working on this myself and plan to do a 6-hour uninterrupted session the next time. Maybe adding some SDS sits into it. The focus must be this:  That 1 day has to be really uninterrupted as to mindfulness application (moving, laying down, sitting etc.) and very high quality. You need to maintain deep states of no-mind basically for whole day.  This attempt also gave me hope that it is possible to thrive in solitary confinement. My experience was not 'thrive' per se because I've still experienced a lot of micro sufferings those 4 hours. I've only minimally suffered thanks to my practice. I've maintained a relatively deep state of no-mind for 4 hours, experienced one salient psychedelic state and survived the whole ordeal without giving up or feeling like this was torture. It was still hard but I've enjoyed it for the most part. I feel more confident now to do longer uninterrupted practices and understand the mind of these advanced yogis taking years-long retreats. I felt like this was a big step in that direction. Hope this report inspired some of you. Feel free to ask me your questions.