The Sikorsky 76C++ is easily the EASIEST heli to fly to an unrealistic extent. Now, the Bo105 and ec135 are very realistic, so I attribute your problem to pilot error. I'm probably not the best person to try to teach you how to fly a heli (Hint hint HHS and Groucho
), but from what I've read, and from my experience, you must make VERY gentle changes in control input to keep them stable. OH! How fast are you flying. If you fly too fast the heli will roll and pitch uncontrollably. I think it is to simulate the structural damage you are about to cause, which isn't actually simulated (yet?).
Let's see, loss of lift. This happens when your RPMs drop. If you have the collective pitch pulled up, are going too fast, and you're pulling up on the cyclic (let's say you accidentally nose-dived) then you should find that the RPMs drop, and you are unable to climb, and then you crash. The trick to get out of that is to carefully reduce collective, NOT TOO MUCH, in order to maintain your RPMs, as you pull on the cyclic. However, if you have nose-dived, your chances of escape are slim.
What else... happens as soon as you lift off. If you try to take off and find the the heli immediately goes into a spin, you have pulled the collective too fast. To recover, slowly reduce the collective while countering the spin with tail rotor force. The heli should eventually stop spinning and become controllable. Be very careful, and avoid lag, since you'll be at a very low altitude when this happens.