You will probably feel the lock handle that you pull on to open the door has squeezed in and jammed in. What I do is lean on the door to push it in, and get my finger under the door latch and try to roll it out back into the normal position while locking and unlocking it with the key - this makes it budge.

When you have it out and from now when you are normally opening the door, make sure the door is unlocked before opening it otherwise it will jam again, and when opening you need to push in on the door before squeezing the handle and opening the door. Since doing it this way I have never had an issue.