Why did Martin Eden live at night with the gods in a colossal nightmare?

Question

Re-reading Jack London's Martin Eden for my project, I've come across this passage:

Martin had ascended from pitch to pitch of intellectual living, and here he was at a higher pitch than ever.  All the hidden things were laying their secrets bare.  He was drunken with comprehension.  At night, asleep, he lived with the gods in colossal nightmare; and awake, in the day, he went around like a somnambulist, with absent stare, gazing upon the world he had just discovered.
_{Martin Eden, chapter XIII. Emphasis mine.}

This appears right after Martin discovers Herbert Spencer, whose works will play a major role in Martin's later life.

I can understand the sentences before the one with highlighted bit; I can also understand why he "went around like a somnambulist".

What I can't understand is the "nightmare" and "gods". If "nightmare" is used in a literal sense here, why would he have nightmares at all, especially with gods?

If the nightmares are meant in a more symbolic sense, then what do they represent? It is stated in the book that Martin resented sleep, seeing it as a waste of time, and thus sleeping for only 5 hours a day (even trying sleeping for only 4 hours, but that was too hard).

I just don't see why Martin would experience anything negative in his sleep, since everything thus far has only been good for him - Ruth, studying, writing, and now Spencer.

Answer 1

Martin has just read Herbert Spencer’s First Principles of a New System of Philosophy (1862), which describes a universal and teleological process of evolution spanning every scale from microscopic to galactic.

Thus from the persistence of force follow, not only the various direct and indirect equilibrations going on around, together with that cosmical equilibration which brings Evolution under all its forms to a close; but also those less manifest equilibrations shown in the re-adjustments of moving equilibria that have been disturbed. By this ultimate principle is proveable the tendency of every organism, disordered by some unusual influence, to return to a balanced state. To it also may be traced the capacity, possessed in a slight degree by individuals, and in a greater degree by species, of becoming adapted to new circumstances. And not less does it afford a basis for the inference, that there is a gradual advance towards harmony between man's mental nature and the conditions of his existence. After finding that from it are deducible the various characteristics of Evolution, we finally draw from it a warrant for the belief, that Evolution can end only in the establishment of the greatest perfection and the most complete happiness.

_{Herbert Spencer (1862). First Principles of a New System of Philosophy, p. 486. London: Williams and Norgate.}

Martin has experienced an intellectual epiphany—his mind has been blown, as we might say nowadays—and he finds it simultaneously exhilarating and terrifying, like standing on the edge of a precipice. His sense of the solidity of his knowledge of the world has been cut out from under him, and he does not know to what conclusion Spencer’s philosophy will lead him.

The metaphor of “living with the gods in colossal nightmare” attempts to convey this combination of exhilaration and terror. The pagan gods are wise and powerful but also fickle and dangerous: to live on Olympus is to risk the thunderbolts of Zeus and the arrows of Artemis.