Multidimensional travel was not as easy on someone's body as normal teleportation. The lack of time and space within the negative zone worked as an interference over the connection formed between the universes, impacting the body of the cultivators right after they would complete their instantaneous travel.
This disturbance was something that affected those who were not used to multidimensional travel. These people would, just like Daniel had after walking through the portal, feel a sense of extreme dizziness take over their minds, and if unable to control their body, be forced to bend forward in order to empty the content of their stomach.
Luckily, Daniel had a perfect control of his body, and while he couldn't avoid the dizziness, he was able to maintain a somewhat dignified posture, and avoid making a spectacle out of himself.