According to the tradition passed down to us from the Baal Shem Tov, the day after Yom Kippur is called the Holiday of G‑d’s Name. As it is explained in Kabbalah and the Chasidic tradition, each Divine name corresponds to a particular emanation of the G‑dly light and is associated with specific worlds and specific sephirot. For example, the name, Ekiyeh (AHYH) is associated with the sephirah of Ketter. The names Havayah (Y‑H‑W‑H) is associated with the world of Atzilut and sephirah of Tiferet, etc. However, when we refer to the Divine Name without specifying which particular name it is, we refer to the level that is higher than all worlds and all sephirot. On Yom Kippur, we reach our very essence, the level of Yehida shebenefesh—the highest level of the Divine soul. This is why, on the day after Yom Kippur, we merit the revelation of the Divine light, which issues from the very essence of the Creator and is higher than all particular levels and gradations.
We see a metaphor for this in cosmology. In the first instances after the Big Bang, the energy was so high that all forces were unified together. Only as the Universe cooled down a bit, this unified force was split into strong and weak nuclear forces, electromagnetic and gravitational forces.
Today, after Yom Kippur, we experience this high octane energy. It is so sublime that there is no specific mitzvah associated with it. We tap into this undifferentiated energy by building our sukkah-booths b’simchah—in state of joy.