This is a situation we all face at one time or another. It feels awful and can feel very scary.
However, it's not what you think it is. It's not the end of things. It only feels that way.
Look at it this way. You've been operating in a room (an analogy for your life or career or whatever), and you've explored all there is to know in that room. It's time to open a door, and walk out into new territories.
But you don't know there is a door that you need to open. You keep walking around that room looking for an answer when the answer is to get out of that room and into new experiences.
You need a brand new idea.
You can't know that idea ahead of time.
You just need to be open to it.
You can know you've come to the end of a road. You don't (yet), know the new road, but knowing there is a new road is enough.
So you sit with great anticipation and excitement for your new life to begin. You stay open to possibilities. You don't force things. You don't get upset that you don't already know. You stay open, happy, excited, enthusiastic.
And, sure enough, someone will say something, you'll see something, a new idea will simply pop into your head and off you go; you found that door and you've gone through it and into your new life.
There is always the next thing for everyone. It's the law of the Universe. There is no reason to be despondent. You just have to know there is something new for you and be patient for its coming.