Three consonants and a dozen vowels 

A humorous way of saying you are exhausted; the word you'd be referring to would be, "Sleeeeeepeeeeee......". If you're more or less tired than that, simply adjust the number of vowels accordingly, such as "three consonants and eight vowels" for being "normally" weary, or "three consonants and TWENTY vowels" for being limply-plastered-on-da-bed zonked.

Weary girl, texting a pleasant-natured willing-to-help-anyone-out dude who's frequently assisted her in the past: Any chance you could come over and help me move this big heavy couch so that I can vacuum the floor underneath it?
Dude: Ummmm... three consonants and a dozen vowels.
Girl: "Sleeeeeepeeeeee"???
Dude: Sumpin' like dat... had a long day. Mebbe first --- yawwwwwn --- first thing tomorrow morning? Gimme a wake-up call when you're up and about?
Girl: Sounds good. And of course I'll need a shower after I finish all da dusty sweeping and vacuuming, so I'll let you take it with me, as an extra incentive and thank-you gesture for your help.
Dude: Nice. Will you also let me crawl in bed wif you after we towel off, and we can enjoy a nice long warm skin-to-skin cuddle-nap together?
Girl: Of course --- what better way to reward ya back, eh??

Three consonants and a dozen vowels by QuacksO August 16, 2018