King Laugh in the Imitation of Christ

The Imitation of Christ 3.6.3 contains this passage: "Keep your intention and your purpose always whole and strong toward Me, and do not think that it is an illusion you are suddenly lifted up to sublime thoughts, and you are soon after turned again to your first levity of heart; for you suffer such levity of heart against your will rather than with your will, and so, if you are displeased by it, it will be of great merit for you, and no loss" (this translation, p. 113).

Here's the Latin from The Latin Library (here).

Forte serva propositum, et intentionem rectam ad Deum. Non est illusio, quod aliquando in excessum subito raperis et statim ad ineptias solitas cordis reverteris. Illas enim magis invite pateris quam agis, et quamdiu displicent, et reniteris, meritum est et non perditio.

The word translated "levity" is ineptia, "foolishness" or "silliness." 

This passage reminded me of another in the novel Dracula (which, you know, happens). It is in Dr. Seward's diary for 22 September, the day of Lucy Westenra's funeral, in chapter 13. After the funeral, when Abraham Van Helsing was alone with his friend, John Seward, the latter reports: 

The moment we were alone in the carriage he gave way to a regular fit of hysterics. He has denied to me since that it was hysterics, and insisted that it was only his sense of humour asserting itself under very terrible conditions. He laughed till he cried, and I had to draw down the blinds lest any one should see us and misjudge; and then he cried, till he laughed again; and laughed and cried together, just as a woman does. I tried to be stern with him, as one is to a woman under the circumstances; but it had no effect.

Dr. Seward was, of course, confused and disturbed by Van Helsing, and not altogether assured by Van Helsing's explanation, part of which is follows (as reported by Seward). 

at such moment King Laugh he come to me and shout and bellow in my ear, ‘Here I am! here I am!’ till the blood come dance back and bring some of the sunshine that he carry with him to my cheek. Oh, friend John, it is a strange world, a sad world, a world full of miseries, and woes, and troubles; and yet when King Laugh come he make them all dance to the tune he play.

I had never given this passage from Dracula much thought; indeed, it's not one of the passages I look forward to hearing, and I sometimes consider skipping it. But finding something similar about the potential dangers of laughter in The Imitation of Christ gave me pause; both Van Helsing and Thomas à Kempis are concerned to acknowledge that sometimes King Laugh takes control, and they want to relieve people of the notion that it's necessarily a sign of low morals. 

Are such discussions a feature of a tradition of morality? Is there a medieval—or, even, ancient—tradition reflecting on uncontrollable or ill-timed laughter, and its relation to morality?