Likutei Moharan 65:4/ליקוטי מוהר"ן ס״ה:ד׳

14. Certainly, at the moment of self-transcendence—that state in which one becomes totally absorbed in the ultimate goal, which is entirely good, entirely one—the suffering is genuinely nullified, as mentioned above. However it is impossible to always remain <on the same spiritual level>, in a permanent state of self-transcendence, since that would entail going beyond the bounds of the human experience. Self-transcendence must therefore be in the aspect of running and returning.

2Thus when the conscious mind returns from the state of self-transcendence to the brain, which is the seat of consciousness, the mentalities—the vessels—are unable to hold the [higher] consciousness of the self-transcendent state. This is because <this [higher] consciousness> is the aspect of Ein Sof, which is the aspect of the ultimate goal: entirely one, entirely good. As a result, the brain feels the pain of the suffering, since it is in the brain that all the sensations of pain and torment are primarily felt, God forbid. Neural passages extend from the brain to all the limbs, through which the brain senses the pain in whichever limb it is located.

3And know, that afterwards, when one[‘s consciousness] returns from the state of self-transcendence to the vessels—namely, the mentalities—the suffering becomes even more intense than before. It is like two people fighting and wrestling with one another. When one sees that the other is gaining the upper hand, he musters greater strength and attacks even harder. Similarly, when the powers of judgment see that a person wants to overcome his suffering and nullify it through total absorption in the ultimate goal, they muster greater strength and attack even harder. Thus later on, when one returns from the state of self-transcendence, the suffering is even greater than before. This is because [the powers of judgment] intensify their fight against him since he wants to escape from them, as explained above.