PC-12
Flight Crew Multiengine; Flight Crew Commercial; Flight Crew Instrument
Situational Awareness; Physiological - Other
Aircraft Equipment Problem Critical; Flight Deck / Cabin / Aircraft Event Illness / Injury
Air Traffic Control Provided Assistance; Flight Crew Diverted; Flight Crew Landed in Emergency Condition
Human Factors; Aircraft
I was in cruise flight at FL 260 and kept hearing a whistling noise from the rear of the pressurized cabin.  Pressurization indications didn't appear to be abnormal but I didn't feel well. I was hot and light headed and felt almost hypoxic. I decided to inform ATC that I wasn't feeling well and needed to divert to ZZZ. I was given a clearance to descend and I put on my oxygen mask and started an emergency descent. I was cleared direct to ZZZ and proceeded to head that way. ATC informed me that they were [providing priority handling] on my behalf and I acknowledged them. I proceeded to descend down to each clearance limit and then made a safe and successful landing at ZZZ.
PC-12 Pilot reported a diversion due to experiencing hypoxia symptoms possibly the result of a pressurization issue.