baby choking 😭

S J B
My baby girl (4weeks old) is scaring  the living daylights out of me! She chokes so much during breastfeeding but tonight it went on for ages and I was so scared I thought she was going to die 😭😭😭! I feel so scared about something happening to her, I have such anxiety I can't stop watching her now after tonight and panicking at every sound she makes! Me and my husband aren't getting along either and I just feel like I've got no one to talk to which isn't helping!! 
Does anyone else's babies do this? And what's the best thing to do when it happens! I always sit her up immediately and lean her forward and pat her back , but that's just an automatic reaction, not sure that's the best thing to do?