Timelessness / Eternal Now

Timelessness — sometimes called atemporality or the Eternal Now — is the phenomenological experience in which ordinary linear temporal sequence appears to dissolve, leaving the experiencer in a state where the categories 'before,' 'after,' and 'now' cease to organise experience in their usual way. Unlike time dilation (in which time seems to slow) or time compression (in which it seems to accelerate), timelessness is the more radical experience of time itself no longer applying.

PsychonautWiki's Subjective Effect Index describes atemporality as a state in which 'the concept of time as a linear or sequential progression is no longer perceived,' with the experiencer instead 'seemingly existing within a single moment that contains all other moments simultaneously.' The specific phenomenology varies substantially — some experiencers describe the moment expanding to contain everything, some describe past and future collapsing into the present, others describe having always been here, with the ordinary sense of a personal history stretching backwards through time appearing suddenly as one thread of a much wider now.

The state is widely reported across contemplative and mystical traditions. The Christian mystic Meister Eckhart wrote extensively about the nunc stans — the standing now — as the mode in which the eternal God is present within time. The Buddhist tradition of the Ekayāna schools speaks of timeless awareness (ye shes, the primordial knowing) as the ground state of mind. The Sufi waqt (the felt Moment) points at the same territory. Contemporary spiritual writers — most prominently Eckhart Tolle, whose The Power of Now (1997) sold twelve million copies — have popularised the concept for wide Western audiences.

In psychedelic and deep-meditative reports, timelessness is one of the most-reported alterations of ordinary consciousness. It is sometimes uncomfortable (particularly on shorter substances where the loss of temporal reference can register as being stuck); it is more often described as an unexpected liberation from the specifically anxious quality of ordinary temporal projection (the constant background awareness of past regret and future concern). Contemporary neuroscience has correlated the state with disruption of the temporal-processing networks in the brain, though the phenomenological content of the state remains — as always with subjective experience — irreducible to its neural correlates.

Sources:
PsychonautWiki — Atemporality
Wikipedia — Eternal present