You should always see a doctor before starting a routine of high-intense workouts as Alexandre Borela said and get their approval. Furthermore, the workouts should start of slow (low-medium intensity) and build up to high intensity. It is not good to start at a high intensity when you are not very regular to it.
Also, don't try jumping on the treadmill while it's on high speed, you will fall. Instead, gradually increase its speed to the point where you want it to be.
When running at high speed, every mistake can launch you off from the treadmill so you need to be at 100% focus on every step you take and never do more than you know you can do just to push yourself. You are more likely to hurt yourself rather than develop anything.
And also use everything that can support you if you do fall- Mattresses around the treadmill, the magnetic autostop clip which JohnP mentioned and even have someone close by in case of falling. Better safe than sorry.