Possibly because it is right in front of you is why you didn't see it. Possibly it has been staring you in the face for so long that you got used to overlooking its gaze. Possibly you didn't want to see it but that isn't like you. And then also: Possibly it isn't there at all and you didn't conjure it OUT of existence so much as you are conjuring it INTO existence now.
So many things are possible.
And maybe it doesn't come down to this one thing at all; maybe it's a bunch of little things adding into this tower of toppling horror. In which case instead of standing there all bravely confronting what you see, your time would be better spent taking apart the pieces, sorting them into piles like you used to do with Legos. Not everybody has to be a builder and especially you don't have to build this up into a giant scary thing. Sometimes it's time to put the toys away; sometimes it's okay to say it's this one little thing and that one little thing and this thing and that thing and they don't have to turn into something bigger than you can solve.
There is not really a box big enough for all these things.
It is not good that this is happening but it is important to remember that it is not happening to you just because you're there for it. You can realize it's not about you. You can realize it's not about anything in fact. You can realize that flipping out was never your strong suit. What are you good at? What are you good for? You can spend some time reflecting on those strengths. What's not up for debate is that you'll need them.