Aristotle [ca. 350 BCE] (De animalibus Book 8, 19.2): The dormouse hibernates in trees and is then very fat... - [Cresswell translation, 1887]

Isidore of Seville [7th century CE] (Etymologies, Book 12, 3:6): Dormice [glis] are so called because sleep makes them fat, for we say that to grows to ‘swell’ [gliscere]. They sleep for the entire winter and lie motionless as if they were dead; in the summertime they revive. - [Barney, Lewis, et. al. translation]

Gerald of Wales [c. 1146 – c. 1223] (Topographia Hibernica, Distinction 1, 15): ...the animals called dormice, because sleep makes them fat (for the word from which they derive their name, gllscere, signifies to grow fat, as well as to long after), sleep all the winter, and, after lying motionless as if they were dead, revive in the summer. - [Forester translation, 1863]

Thomas of Cantimpré [circa 1200-1272 CE] (Liber de natura rerum, Quadrupeds 4.46): The dormouse [glis], as he says [i.e. Liber rerum], is a small animal, varied in white, black, and red. During the whole winter it sleeps and lies as a compacted ball, and in a strange way, as Isidore says, it grows fat in its very sleep. He then explains how this is done. For it is impossible for an animal to live without breathing, even if breathing is said to be a hidden or manifest intake of air for the suppression of innate heat. But still, that little fire is so small, that it needs fuel rather than tempering. Wherefore for such animals the air is sufficient that only by enters through the pores. For this is necessary too, that no food is taken by them, because the lingering heat is rather suffocated by food than feeding the heat. And there is another reason: where nothing is lost, nothing needs to be repaired. But in these animals there is no consumption of the members either from external heat or internal heat. Hence there is no need for repair. This is the same reason in the case of the stork, that while it is very cold, in the winter the places it chooses from its mixture, that is to say, waters, it sometimes seeks and immerses itself in them, and, constricted by the cold, lies almost dead. Afterward, when the warmth of the season arrives, it naturally rises up and goes out into the waters, and after washing the mud from itself, it returns to life. In these words we will proceed further to the nature of the gliris. And so at the coming of spring, when the sun has emitted warm rays, the beast naturally returns to its strength. Another reason why it can live without food in the winter is that the animal is very cold and has little heat and thick fluids, which are not consumed by the heat of a very small fire. it runs in the trees as if on the ground, and delights more eagerly in the juice of apples. Pliny says that it will be beneficial for those who fear paralysis to use a decoction of the fat of the dormouse smeared on the limbs. - [Badke translation/paraphrase]

Bartholomaeus Anglicus [13th century CE] (Liber de proprietatibus rerum, Book18.56): Glires bée lyttle beastes, as it were great Mice and have that name Glires, for sléepe make them fat. And Gliscefe is for to ware, as Isidore sayeth, and hée sléepeth all the Winter unmoveable, and telleth as though he were dead, and quickneth again in Summer time, as he sayth, libro. 8. cap. 57. Plinius speaketh of these Glires, and sayth, that they dwell gladly in woods, and love their fellowes that they know, and strive & fight against other, & they love their sires with great mildnesse & pitie, and féed and serve them in their age. - [Batman]