Well, it is something that people do to cleanse their body. I know of woman who spent two weeks drinking water only, whilst lying down all the time. If it was my guess, I would suppose that she came out of this pretty feeble, but for her body, it must have been a very cleansing experience.
But, it can also be applied to someone's mind. One technique that is socially acceptable is relaxation. First, you have to be completely relaxed and this is done by relaxing your muscles from your toes, feet to legs onward all the way up to your head. Then, that is when it gets tricky because there many different ways to achieve the same thing.
One way is that someone should attempt empty her/his mind of all thoughts and thinking about herself/himself and vizualized one surrounded in light blue light or feel like one is suspended or floating on air,or on a really, really comfortable mattress.
This technique is accomplished usually by lying down on a mat on the floor.
There is another way of purging oneself once in this relaxed state. Many things of "imaging" can be achieved: one of them is to see yourself going away on a plane with a lot of luggages. As you are flying above the earth, you throw away one luggage, then a heavy bag and end up without any luggages on a beautiful seashore under the son and lying on warm sand, or maybe under a tree or watetever you can imagine or dream about. This can usually be vizualized easily enough. And there are a lot of others vizualization techniques.
But,what about doing or going about it more deliberately ?
Maybe,you first think about what's bothering you and what's getting you worried now, today, this week or for the last weeks or longer, and then examine if there is a pattern to it; what is most prominent, and then try to analyze it for as long as it takes you ; to view it from different angles; and this, not only from your own perspective but trying to see it from another one point of view, from an outsider one (always without ever asking anyone about it). Then you process it , you try to dissect it and this leads you further...
You can then maybe find alternatives or different ways to look at it and to think about it from a different and hopefully better view point...
For me, that is a fresh way to start this process through this view point and to come to a different conclusion. For others, this whole process might be entirely different... But to be able to look, hear, understand things, your own problems, whatever comes about, ideas, opinions, differently can be a great start... And also, to be able to halt the purging (and renewing) process when one becomes overwhelmed or feel the need to slow it down can also be necessary.
Well, this is a personal experience and thoughts, and I am pretty sure that many therapists and psychologists have thought and written about it much already, in a more deeply approach...
For me it is a step towards discovery about oneself and also understanding the world better (well, especially the part about purging one's mind). The other techniques may also achieve much good for one's body and mind, but I also like a lot the one about going inside one's head, since it appears to me to be done very consciously.