never had any real problems with it. although once, the night before I was expecting to roll, my friend and I both took 300mg before bed. we both had nightmares (lower doses had previously just produced more lucid dreams). we both also reported a very strange feeling of uncontrollable inertia (in our nightmares).
for instance, in these dreams, if we tilted our head it would gain momentum. It would feel as if it was made of concrete and would pull the rest of our body to the ground. we felt like we were stuck in a spot and when we finally were able to move, we would be flung into the direction we started moving without any way to slow ourselves down.