I wasn't really sure how to fix it and all the guides I could find were for stretching teeshirts that had shrunk. I did try boiling it to see if it would shrink but that simply killed the rest of the lycra :0
I measured about 2 1/5 inches from the top seam, ran a zigzag stitch all the way along and then added a simple straight seam. The nerve racking bit was cutting off the excess fabric but I made the cut and it worked perfectly.
The back edge of the top was left raw so I turned it under and tacked it.
Then I got a little adventurous and snipped off the lace edging that was looking a bit grey and sad. Next I added some ribbon that I had left over from Christmas.
I tacked the ribbon in place to ensure it wouldn't slip on the machine and then striched it place with two lines of stitching. Before machine stictching I did check I could definitely get my head through the resized hole! My favourite pajamas are now restored and I can wear them without disgracing myself!!