The Annotated Nexus - Pages 41, 42
41.1 "high unfathomable ache of emptiness into which all creation might be poured and still it would be emptiness"
Miller places this phrase in quotations, but I can't find the source for it. Miller follows this by saying "this aching for God, as it has been called." Perhaps he's quoted an obscure religious text. Miller believes this aptly describes "the soul's loveless state." To explore these views in a larger context of Nexus and The Rosy Crucifixion, take a look at Chris Light's essay, Art And The Artist in The Rosy Crucifixion [PDF].
41.2 rack and wheel
Miller has entered the loveless state described above, "fully equipped with rack and wheel." This could have two meanings. First, he could be referring to the rack and wheel structure of a bicycle, implying that he foolishly raced headlong into the current situation (he follows this by commenting on how alarmingly fast "events piled up"). Secondly, he could be referencing the mediaeval torture devices of rack and wheel; this is consistent with his self-portrayal as a lovefool who is a glutton for punishment in his relationship with Mona/June.
This is a continuation of the idea of the "mind machine" (also mentioned in this paragraph) state of being, which he first introduced on Page 38.
For those of you in the warmer tropical zones, a toboggan is a snow slide, sled or sleigh. An Olympic bobsleigh is technically a toboggan, so you know what kind of barely-controllable momentum we're talking about here. Miller is comparing a toboggan ride to the journey to self-destruction we take when he go into a "mind machine" state. As long as there is a "flicker of life," the mind machine ploughs forward without being slowed by any other self-regulating emotional factors; in fact, he is an empty vessel (a "victim") into which any "demon" may take possession.
41.5 "this side of Paradise"
Miller compares life inside the "vacuum of the mind" to "this side of Paradise," which he places in quotes. Although these words are more famously attributed to F. Scott Fitzgerald's first novel of that name (1920), it originated with the poet Rupert Brooke, and his poem Tiare Tahiti (1914).
As I interpret it, Brooke's line is meant to dileniate the pleasures of earthly life (this side) from the "paradise" of an afterlife (that side). The "wise," Brooke claims, agree that Paradise exists after death; therefore, in the primal pleasures of "this side of Paradise" there is "little comfort in the wise." Miller, then, is saying that he is locked into a pursuit of reckless passion without wisdom.
41.6 St. Vitus' Dance
Miller is so deeply into "this side of Paradise"/"the mind machine" "that even the rigor of death seems like a St. Vitus' Dance." The St. Vitus Dance is a neurological disorder now identified as chorea, in which the victim suffers involuntary, almost-rhythmic muscular jerks. In Mediaeval times, the condition was named after Vitus, patron saint of dancers (as well as actors and comedians). Miller's metaphor, then, describes someone in such a state of passionate auto-pilot, that not even death itself would cause him to rest. As he states in the following paragraph, after equating himself to a dead horse galloping in a void, "I kept galloping to the farthest corners of the universe and nowhere finding peace, comfort or rest."