If you place a police officer under citizen's arrest, does that officer still hold the authority to arrest you?
While it is from a different jurisdiction, the following goes to the heart of the matter:
Arrest, when used in its ordinary and natural sense, means the apprehension of a person or the deprivation of a person's liberty. The question whether the person is under arrest or not depends not on the legality of the arrest, but on whether the person has been deprived of personal liberty of movement.
Directorate of Enforcement v Deepak Mahajan, (1994) 3 SCC 440 at ¶46 (SC of India)
In your example, the police officer has been deprived of "personal liberty of movement"; if they can still speak there would be no legal impediment to them placing the person who arrested them also under arrest.
It would then be incumbent on both parties to deliver each other into lawful custody. The citizen would need to seek out a law enforcement officer to do this; the police officer has already done so, being their own law enforcement officer.
After this, comes the paperwork.