If you have cpr or aed training…and a person is unconscious, consent is implied. Especially if you follow training. You felt for a pulse and/or they were not breathing, you will not get sued in this country. If someone manages to get it to court, they will lose.
I am a certified CPR and AED , a registered WFR and just had a training class on the matter. As long as you follow proper protocol you are ok. And I’d like to add, as a man, yeah, I’d be nervous also exposing a womans chest in a crowd, people are stupid, but you can probably save a life.