From the Lesser Thousand Worlds to the Myriad Heavens.
Feeling uncomfortable was perfectly normal.
Though spiritual energy and Dou Qi were similar in nature, both being energy drawn from heaven and earth, spiritual energy of the same level was of a higher quality than Dou Qi. Moreover, because the Myriad Heavens and Lesser Thousand Worlds had different limits and degrees of completeness, although they were things of the same nature, Dou Qi undoubtedly lacked just a little nourishment compared to spiritual energy.
It was like two stalks of wheat in a field.
One was fertilized, while the other was not.
Naturally, the wheat they produced would be different.
Therefore, ascending from a Lesser Thousand World to the Myriad Heavens and converting Dou Qi into spiritual energy was an extremely difficult process. During that process, cultivators with higher realms had to put in more effort and bear greater risks than weaker cultivators. However, descending from the Myriad Heavens into a Lesser Thousand World did not require converting spiritual energy into Dou Qi. Even the spiritual energy itself retained its proper might and would not be assimilated by the Lesser Thousand World's Heaven and Earth Power.
This was also why those Heavenly Sovereigns from the Myriad Heavens could utterly crush the Extraterrestrial Evil Gods invading Lesser Thousand Worlds during their patrols. Even when those Extraterrestrial Evil Gods used techniques to summon their ancestors, they still could not defeat those Heavenly Sovereigns.
The upper limit of a Lesser Thousand World's development was the Earth Supreme realm.
At most, an Earth Supreme could summon a Heavenly Sovereign.
Moreover, because the Earth Supreme himself used power belonging to the current Lesser Thousand World for the summoning, the Heavenly Sovereign he summoned would most likely possess only the might of an Earth Supreme at Great Perfection.