Date: 202108
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Flight conditions: VMC
Light: Daylight
Aircraft: B737-800
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Climb
Airspace: Class B ZZZ
ATC / advisory: Center ZZZZ1
Aircraft component: Exterior Pax/Crew Door
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Flight Attendant (On Duty); Flight Attendant In Charge
Reporter qualification: Flight Attendant Current
Human factors: Communication Breakdown; Troubleshooting; Situational Awareness
Anomaly: Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural FAR; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Flight Attendant
When detected: In-flight
Result: Air Traffic Control Provided Assistance; Flight Crew Landed As Precaution; Flight Crew Requested ATC Assistance / Clarification; Flight Crew Took Evasive Action; General Maintenance Action
Contributing factors: Aircraft; Procedure
Primary problem: Procedure

Narrative: Working flight ZZZ to ZZZ1. I was working the A position. Was having a hard time closing one door. Tried several attempts on it. Finally that he stepped in to try to close the door forced herself with her body to close it. Even after we close the door it still did not feel right. After closing the door the Captain called back and asked me to disarm my door and reopen it . He said it did not sound right during door closure. That he heard a weird sound as the door was closing. After reopening the door the agent said that the door closure did not look right and there was the hinge from the door that was sticking it out. I re closed the door. Still having a hard time closing the door.  The Captain decided to call maintenance out to have it checked since it still didn't sound right during door closure . Maintenance asked ' what's the problem '. I explained what the door issue was and he said it was fine.  I work the A position all the time closed and opened that L- door time after time and I know when I know that it didn't feel right when I closed it. [Procedures] not at play here.After take off both the D and  I started hearing a 'swoosh' noise coming from the L-1 door. I was thinking that at 10;000 feet the door would seal and the sound would go away. I could hear very light air coming from above side of the Ali door. I told my D that doesn't sound right.I started feeling a my chest getting heavy; my heart started racing; my head started hurting. I told my D something is wrong. I started  seeing almost like tunnel vision darkness and stars. The next thing I  remember the D took me out of my jump seat put me in oxygen in seat X.  After two puffs of oxygen I started to feel better.I have no idea what altitude we were at. But I do know that something was Very wrong. Captain playing around and return to ZZZ. We had medics meet the flight to check on me. I did not land in my jump seat under the Circumstances.




Synopsis: During door closure for departure; Flight Attendant reported a door did not close properly and was advised by maintenance there was no problem. In flight; the door began leaking and the Flight Attendant became incapacitated; resulting in an air turn back.