Dimensional fatigue — also Inter-Dimensional Fatigue, or IDF — is a process or force that weakens the boundaries between dimensions. It is most often used to access HyperSpace from TrueSpace. Dimensional Fatigue can be projected by devices, and occasionally occurs naturally.
IDF research is believed to be incredibly dangerous, a stance strongly supported by the Arilou. Indeed, most races that use HyperSpace either had the technology gifted to them by a patron, or somehow inherited the technology from elsewhere.
The Chenjesu were naturally attuned to HyperSpace, and may have been one of the few races to develop the technology on their own. While the Yehat are known to have achieved inter-planetary travel on their own, as did the Humans, neither race independently deveoloped HyperSpace technology. However, a human offshoot culture, the Androsynth, did seem to do so, although they may have received the technology via covert contact with some other race. The Androsynth continued IDF research after departing Earth, but were destroyed utterly, perhaps by the Orz, possibly because their research attracted that race's attention.
The Taalo, a member race of the Sentient Milieu which disappeared long ago, were known to work in IDF and had experemental sites in the same area of space that has since been occupied by the Androsynth and Orz. Some of their research materials and other technologies can still be found there.
It is possible that the Arilou are lying about the danger involved in continued IDF research for their own inscrutable purposes; perhaps to keep the secret of QuasiSpace from becomming general knowledge. However, it is undeniable that HyperSpace travel has not been invented more than a handfull of times, and that some catastrophe indeed befell the Androsynth.