A321 pilot reported master caution indication for over wing door during climb. Flight returned to departure airport for uneventful landing.

Narrative

Flight 1 (Day 0)ZZZ-ZZZ1CA: Person A Pilot Monitoring FO: Person B Pilot FlyingFlight Summary: Nice aircraft; clean maintenance book. Beautiful day departing ZZZ. Short taxi and uneventful takeoff.Event Description:During climb-out; at approximately 7;500 feet; we received a Master Caution for an overwing exit door. The Master Caution was canceled; and we checked the pressurization system before deciding to level off. Pressurization was normal; so I instructed the FO to continue the climb. Shortly afterward; the ECAM message cleared before we had the chance to address it. At approximately 14;000 feet; we received another Master Caution for the same overwing exit door. We canceled the caution again. This time; I instructed the FO to level off at 15;000 and checked the pressurization system page. Pressurization again appeared normal; with cabin altitude around 1;100 feet. At that moment; the Number 1 Inflight called the flight deck; reporting that they had heard three high chime bells accompanied by a red blinking light on their flight attendant panel. Familiar with this common issue from prior experience; I instructed the inflight crew to verify that the overwing emergency exit door handle cover was properly secured. They confirmed it was not fully in place; reseated it; and the white slide door light; Master Caution; and ECAM message all cleared. While the inflight crew was checking and securing the door handle cover; I began reviewing the QRH. Suddenly; I experienced heaviness in my arms; blurry vision; and slurred speech. I immediately instructed the FO to don his oxygen mask; which I did as well. We advised ATC and initiated a descent below 10;000 feet. Once below 10;000 feet; we removed our masks; and I began feeling better. I asked the FO to inform ATC that we were returning to ZZZ and to request a hold while we sorted out the situation and prepared for the approach. En route to the hold; I called the inflight crew to inform them of the descent and possible diversion; and to check on their condition. The Number 1 inflight reported that the Number 2 was feeling clammy hands and tingling; and the Number 4 was also experiencing tingling and feeling unwell. The FO reported that he was feeling fine. I contacted Dispatch to report the situation and requested to be patched through to Maintenance Control. Maintenance advised that if the door was not leaking and pressurization was normal; they saw no technical reason to discontinue the flight. They offered to patch me to the Duty Pilot for a second opinion; which I accepted. After discussing the situation; including the physiological symptoms experienced by myself and several inflight crew members; the Duty Pilot and I agreed that it was best to return to ZZZ. We were assigned holding at ZZZZZ at 7;000 feet. While in the hold; we set up for the approach; completed all required checklists; including the Overweight Landing Checklist; as we were projected to land above maximum landing weight (174;606 lbs. for our variant). We reviewed all procedures to ensure nothing was missed and that we were ready for the approach. I also called the inflight crew again to brief them on the situation; estimated landing time; and issued a briefing. The approach and landing were uneventful; and we ultimately landed below maximum landing weight at 173;900 lbs. After landing; ATC inquired if we required further assistance; we declined and taxied to Gate XX.Two write-ups were entered in the maintenance logbook: 1 To inspect the overwing exit door/handle cover. 2 To record the landing weight; as requested by Maintenance.Follow-up calls were received from the Duty Pilot to check on crew well being and to offer assistance.