Don't worry... it's totally normal.
When you don't use, well any mop, for a long time they do that.
Provided that you have a quality ink/paint in them.
I don't know the scientific nature of the event, but I do know that
it does happen, and it's normal. Just take the cap, not the the nib,
off and GENTLY push the body back to a somewhat normal position.
Don't force it all the way back to normal if it doesn't want to go back.
If you do that, then it will pull back in and squeeze out ink all over you.
But it is normal. You could empty it and then force it back to normal and
let it sit, but I don't think you need to do that. Good luck!