OK So I have just also looked up Cogentin, and I do understand what this is doing, partly because it is an anticholinergic, and partly because this group of drugs has been discussed here, over quite some period of time. (I have used one and had positive effect, but it was not a drug specifically for PD). They do have a role in the treatment of PD, and before l-dopa were in fact one of the few helpful classes of medication. It seems likely this is why you are having problems.

You have only a short time before your scan. (Is this a DatScan?)

Another way of doing things would be to stick with what you are doing and take very great care of yourself until after your scan, and talk to your your neuro about what you take afterwards. It looks as though you are going through some kind of withdrawal, as well as a return of PD symptoms.

If you get any really unusual like sweating really heavily, raised temperature, headaches etc. please get medical help quickly, and let them know what you have been doing with your meds.