It takes HP to kill things and they give you exactly as much XP back. Some levels take more XP than you have HP. That essentially neans you need to find either chests or healing packs before you run out of that. If you don't get lucky and get more than 2 healing paxks close to spawn it's just not possible to reach more than 10hp for example
You can maximize your chanxes of finding healing packs by always killing as many monsters as you can but that's still not a guarantee.
Or ta least that's what i've been trying, what your strategy? So far i've only managed one win.