He fancied it to be the symptoms of some approaching mental collapse, but, as the weeks went by and nothing unusual occurred, he became used to it, and refused to let it worry him.

If it made his head feel queer to read, the remedy was easy enough--he simply would not read; and though he had been a great reader, and at one time had been used to spend many delightful afternoons lost in the pages of a novel, he now gave it all up with an easy indifference.
But, besides all this, the attack had left him with nerves all unstrung; even his little afternoon walk on Kearney and Market streets exhausted him; any trifling and sudden noise, the closing of a door, the striking of a clock, would cause him to start from his place with a gasp and a quick catch at the heart.

Toward evening this little spasm of nerves would sometimes come upon him even when there was nothing to cause it, and now he could no longer drop off to sleep without first undergoing a whole series of these recoils and starts, that would sometimes bring him violently up to a sitting posture, his breath coming short and quick, his heart galloping, startled at he knew not what.
At first he had intended to see a doctor, but he had put off carrying his intention into effect until he had grown accustomed to the whole matter; otherwise, he was well enough, his appetite was good, and when he finally did get to sleep he would not wake up for a good eight hours.
One evening, however, about three months after the first crisis and just as Vandover was becoming well accustomed to the condition of body and mind in which it had left him, the second attack came on.

It was fearful, much worse than on the first occasion, and this time there was no room for doubt.

Vandover knew that for the moment he was actually insane.
Ellis had been with Vandover most of that afternoon, the two had been playing cards in Vandover's room until nearly six o'clock.