You have implied permission to perform first aid and rescue techniques if the person can't tell you not to. Good Samaritan laws protect you from anything but direct negligence. If you have first aid/cpr certification then you're even better off. That's only in the US, however.
Also, trying to rescue someone in that position is a lot like any problem. Once you touch it, you own it. Negligence would be leaving before the paramedics arrive, /unless/ you can prove you were in imminent danger if you stayed.
Also, trying to rescue someone in that position is a lot like any problem. Once you touch it, you own it. Negligence would be leaving before the paramedics arrive, /unless/ you can prove you were in imminent danger if you stayed.