Got an awful scare this morning,we found a lump on Spice at about 7.30 we were both sure it wasn't there last night

we rushed her to the vet as soon as they opened and it's been confirmed it's a phantom pregnancy following on from her spey!
Poor little thing is now curled up fast asleep having been prodded and stabbed with an antibiotic. We have tablets to give her twice daily from tomorrow and her check up is next Tues.
Can this sort of thing occur again? Is it a common occurance following a spey or do you think it is a ' one off' ? I did suspect her lump was due to this but it was very worrying just the same.
Jacqueline :)