Aleister Crowley distinguished between two main types of egolessness, which he called Dhyana (which also means a method of attaining this state) and Samadhi. He wrote the following about the relative difficulties of attaining them:

One feels "sure" that one can walk a mile along a level road. One knows the conditions, and it would have to be a very extraordinary set of circumstances that would stop one. But though it would be equally fair to say: "I have climbed the Matterhorn and I know I can climb it again," yet there are all sorts of more or less probable circumstances any one of which would prevent success. Now we do know this, that if thought is kept single and steady, Dhyana results. We do not know whether an intensification of this is sufficient to cause Samadhi, or whether some other circumstances are required. One is science, the other empiricism.

http://www.hermetic.com/crowley/aba/aba1.html

Despite this, Crowley recommended a complex system of practices from Eastern and Western sources to help people attain Samadhi of the second type described later, which he associates with the Nothing, or in Hebrew AIN. Although he often talks about summoning spirits, he calls many of these practices romantic forms of dharana or concentration. One can doubt that he ever believed in literal, empirically meaningless spirits, except perhaps during practices that require suspension of disbelief. In reading Crowley's descriptions of 'mystic states', please remember that his use of religious terminology does not imply acceptance of any religious theory.

12. The word Dhyana is difficult to define; it is used by many writers in quite contrary senses. The question is discussed at some length in Part I. of my Book IV. I will quote what I have written about it in conclusion:
'Let us try a final definition. Dhyana resembles Samadhi in many respects. There is a union of the ego and the non-ego, and a loss of the sense of time and space and causality. Duality in any form is abolished. The idea of time involves that of two consecutive things, that of space two non-coincident things, that of causality two connected things.'
14. As Dhyana also represents the condition of annihilation of dividuality, it is a little difficult to distinguish between it and Samadhi[or Atmadarshana]. I wrote in Part I., Book IV.-
'These Dhyanic conditions contradict those of normal thought, but in Samadhi they are very much more marked than in Dhyana. And while in the latter it seems like a simple union of two things, in the former it appears as if all things rush together and unite. One might say this, that in Dhyana there was still this quality latent, that the one existing was opposed to the many non-existing; in Samadhi the many and the one are united in a union of existence with non-existence. This definition is not made from reflection, but from memory.'
15. But that was written in 1911, and since then I have had an immense harvest of experience. I am inclined to say at this moment that Dhyana stands to Samadhi rather as the jumping about like a frog, described in a previous lecture, does to Levitation. [He says, in this previous lecture, he has not confirmed scientifically that one can levitate.] In other words, Dhyana is an unbalanced or an impure approximation to Samadhi. Subject and object unite and disappear with ecstasy mounting to indifference, and so forth, but there is still a presentation of some kind in the new genus of consciousness. In this view Dhyana would be rather like an explosion of gunpowder carelessly mixed; most of it goes off with a bang, but there is some debris of the original components.

http://www.hermetic.com/crowley/yoga/8yoga5.html

Crowley contrasts this kind of Samadhi, which he calls Atmadarshana, with another kind he calls Shivadarshana:

Of this vision what can one say, save that the Universe, as previously known through Atmadarshana, is annihilated? Yet the negation of this phrase is only apparent; the sense is that all that negative Atmadarshana is destroyed; it is only an illusion that goes. Yet there is indeed Nothing in its place -- and the only way to express the matter is to spell that Nothing with a capital N.
If the rationalist reader has had the quite super-Stylite patience to read to this point, he will surely now at last throw down the book with an ethically justifiable curse.
Yet I beg him to believe that there is a shade of difference between me and a paradox-monger. I am not playing with words -- Lord knows how I wish I could! I find that they play with me! -- I am honestly and soberly trying to set down that which I know, that which I know better than I know anything else in the world, that which so transcends and excels all other experience that I am all on fire to proclaim it.
Yet I fail utterly. I have given my life to the study of the English language; I am supposed by my flatterers to have some little facility of expression, especially, one may agree, in conveying the extremes of thought of all kinds. Yet here I want to burn down the Universe for lack of a language.
So the angry mood passes, and one understands how one's predecessors, in the same predicament, got out of it by quietly painting a "Heart girt with a Serpent," or a "Winged Globe" or some similar device…
We are at the end of our little digression upon mystic states, and may cheerfully return to the consideration of Scientific Illuminism. We have had, you may say, a poor half-pennyworth of Science to an intolerable deal of Illuminism. Well, that is what I wanted you to say. Were it not so, I would not have spent these two nights over this paper…
Here, gentlemen, are a number of genuine mystic states; some home-grown, some imported. Please tell us what they are! (You are fond of telling us what things are.)

http://users.lycaeum.org/~sputnik/Ludlow/Texts/Rats/psych.html