אִם־אֶסַּ֣ק שָׁ֭מַיִם שָׁ֣ם אָ֑תָּה וְאַצִּ֖יעָה שְּׁא֣וֹל הִנֶּֽךָּ׃
If I ascend up into heaven, Thou art there; If I make my bed in the nether-world, behold, Thou art there.
Rashi on Psalms
and if I make my bed Heb. ואציעה, an expression of a spread (מצע) and a bed.