Master Flea by E.T.A. Hoffmann

He who has experienced such things in one evening as Mr. Peregrine Tyss, and who is consequently in such a state of mind, cannot possibly sleep well. He rolled about restless on his bed, and, when he fell into that sort of delirium which usually precedes sleep, he again held the little creature in his arms, and felt warm glowing kisses on his lips. Then he would start up and fancy, even when awake, that he heard the sweet voice of Alina. He would burn with desire that she might not have fled, and yet again would fear that she might return and snare him in a net, from which he could not extricate himself. This war of contrary feelings straightened his breast, and filled it at the same time with a sweet pain, such as he had never felt before.

"Sleep not, Peregrine; sleep not, generous man: I must speak with you directly," was lisped close by Peregrine, and still the voice went on with "sleep not, sleep not," till at last he opened his eyes, which he had closed only to see Alina more distinctly. By the light of the lamp he perceived a little monster, scarce a span long, that sat upon the white counterpane, and which at first terrified him, but in the next moment he grasped boldly at it with his hand, to convince himself whether he was or was not deceived by his fancy, but the little monster had immediately disappeared without leaving a trace behind.