The children, aged 13 to 15, shocked other pupils at the Suwan Kiriwong School in Prabaramee Road, Patong, when they began collapsing during the playing of the national anthem soon after 8am today.
Twenty-two were treated in the emergency room at Patong Hospital and allowed to leave. One was kept for further observation.
Parents took other children home after the rare case of mass hysteria interrupted the normal morning ceremony at the school.
Of the 22 students taken to hospital, 21 were girls.
One explanation offered for the students collapsing was a visit to a camp in Khao Lak, north of Phuket, last Friday.
One student is reported to have hung her sarong above head-height - considered to be a slight to tradition. Later, other students saw the ghost of an old woman sitting on the student's shoulder.
A teacher, informed about the strange occurrence, declined to take the paranormal sighting seriously. As a result, nothing was done to appease the old woman's spirit.
At the hospital, the children were told to ''think good thoughts'' about parents and monks and to keep their minds free of ideas about ghosts.
Cases of mass hysteria are relatively rare but have been noted before in the Phuket-Phang Nga region.