You're not alone.
I wonder if it's the whole Mercury in retrograde thing. Anyone know if that affects hormones too? I mean, I'm really not a believer in astrology, but I've gotta say there've been a lot of mechanical glitches recently, of the sort blamed on Mercury in retrograde, and they all started happening after I heard about Mercury going into retrograde. And writers who believe in that stuff are saying it also affects creativity, especially of the first-draft sort.
But, yeah, I so feel (or, in this case, don't feel) what you're going through. I've been thinking the same thing for quite a while, every time I think about writing a major sex scene, and just can't get into it.
At the moment, I'm doing second-draft edits, which doesn't require a whole heck of a lot of passion, just a bit of boring persistence. If you've got a project in that stage, maybe working on it would help get you past this phase.
And if it IS the effect of Mercury in Retrograde, that's supposed to end somewhere around the end of the month, so relief is in sight.
JD