Swelling may come and go for two or three days if it continues more than that, it should be checked. I understand that by Therapy you mean Physiotherapy only and I hope you're consulting a qualified BPT or MPT professional only, if so you may discuss further with the Physio.
Next Steps
You may take another Physio Consultation if this problem persists for longer.
Health Tips
Continue the rehabilitation as it is essential, few ups and downs are seen during rehab so can observe for some time.