What does "crevasse" mean or refer to in this sentence?

Question

I looked into the dictionary that a "crevasse" usually means 'a very deep crack in the thick ice of a glacier', but which could certainly not fit the context. At first it really confuses me, then I guess there are two possible explanations:

1) it refers to 'the small crack/slit of Will‘s half closing eyelids', as his eyelids grew heavier.

2) it refers to 'the break/gap in his words', as he only half finished his sentence before he went deep into sleep.

3) other explanations that I don't know.

Could any one help with this? And I also wonder if it's quite an often/common usage in English, after all, in my opinion, 'crevasse' should refer to large and deep gaps. Why does the author choose this word?

The context is:

Will and 'I' were on holiday, in a hotel with view to ocean, just before Will fell asleep, we were lying in bed, watching the storm and lightening and heavy rain out at sea. Will is a quadriplegic and I am his carer. I found out that he decided to go on euthanasia and I did everything I could in order to change his mind, including this holiday, hoping to make him happy.

Here is the sentence:

Finally, I turned on to my side, away from the sea, and gazed at Will. He turned his head to look back at me in the dim light, and I felt he was telling me the same thing. It’s going to be okay. For the first time in my life I tried not to think about the future. I tried to just be, to simply let the evening’s sensations travel through me. I can’t say how long we stayed like that, just gazing at each other, but gradually Will’s eyelids grew heavier, until he murmured apologetically that he thought he might . . . His breathing deepened, he tipped over that small crevasse into sleep, and then it was just me watching his face, looking at the way his eyelashes separated into little points near the corner of his eyes, at the new freckles on his nose.

Me Before You by Jojo Moyes

Answer 1

This is a metaphorical use of "crevasse". It is comparing sleep and wakefulness - and the difference between them - to a very deep crack in the thick ice of a glacier like you said. So it is saying that he basically fell over the crevasse.

Being awake is the glacier, and being asleep is either the crevasse itself or the glacier on the other side of the crevasse. So when he tipped over the crevasse, his sleep was like that of a glacier and the gap was as wide as a glacier's crevasse.

Answer 2

It seems to me that the word "crevasse" is used to figuratively show the difference in states: wakefulness, and sleeping state. On the one hand - from the material position - the same person, in the same place. Therefore - this small. On the other hand, this is immense - here’s the person, but now he is gone. He fell into the abyss. In the " crevasse".

I think that this is not a typical use of the word "crevasse".

Maybe wrong.

Answer 3

We usually say 'fall asleep'. The writer might have said 'His breathing deepened, he fell asleep', but is using a specific image of 'falling'. I don't think it's a very good image, because in real life you don't 'tip over' a crevasse, you fall or plummet into one.