Trance and Waking
Given that the viewer, SL itself, and the typical home internet connection can all be somewhat unstable, people new to trancing are often concerned about the possibility of losing their connection in the middle of a trance. Luckily, you can't get "stuck" in trance. If your connection (or your hypnotist's connection) goes away, then once you get bored with staring at a screen with nothing happening, you'll either wake up, or the trance will convert to normal sleep.Similarly, if something should happen in RL that demands your attention, you'll find you can break out of trance. This is actually a familiar experience to many people. If you've ever been driving on a highway and have let your mind start to wander, and a few minutes later suddenly realized that you don't remember passing the last few exits, then you've experienced a natural trance, and a very common one. If something unexpected were to happen while you were daydreaming - another driver suddenly pulls out in front of you, for example - you would likely find yourself suddenly back at the wheel and having to deal with the situation. This is exactly the same as abruptly waking yourself up from hypnosis, except that as a hypnotic trance is likely considerably deeper than a natural "highway trance", suddenly waking up from it can be even more disorienting. Fortunately, you're unlikely to find yourself suddenly having to perform an evasive driving maneuver upon waking from hypnosis. But if the phone rings, or an alarm goes off, you'll likely find that you're jerked abruptly out of trance, and it may take a moment or two before you regain your bearings.
Those are probably two of the three most frequently-voiced concerns of a novice trancer. The third is around what the hypnotist might get you to do. And that's very much up to you.
Suggestions
You don't "lose control" in trance. You retain the ability to refuse to do what your hypnotist is asking. And if something is suggested in trance that upsets you, it may well cause you to wake up from the trance. However, in trance you are much more suggestible than usual (which, after all, is one of the main reasons that trance is interesting) and that does leave you more open to being tricked into doing something you might not be comfortable with. And this is one reason that it's important to establish some level of trust in your hypnotist before letting them trance you.Trust and Infatuation
Trust is deeply entwined with what I consider to be the biggest risk associated with hypnosis, and especially with erotic hypnosis, which covers the overwhelming majority of hypnosis in SL. You need to have some level of trust in your hypnotist in order to let the hypnosis work at all, and as I said above, it's a very good idea to make sure that they deserve that trust before you sit down with them, because the very act of being hypnotized by someone will likely serve to increase your trust in them, regardless of whether that trust is actually deserved. This increase in trust happens whenever you share positive experiences with someone - it's how normal relationships are built. The sort of sharing that happens via hypnosis, particularly erotic hypnosis, can be very intense and very intimate, and it's very easy for this shared intimacy and quickly growing trust to develop into an infatuation. While I think it's far more common for someone to become infatuated with their hypnotist than the other way around (if for no other reason than because typically a hypnotist will have multiple "hypno-partners", whereas many subjects will limit themselves to a single hypnotist) it can happen in either direction.Addiction
The possibility of infatuation discussed above is probably an unavoidable danger of erotic hypnosis, especially when you perform multiple trances with the same partner. However, the likelihood is significantly increased with the practice by some hypnotists of deliberately adding "addiction" themes and suggestions to their trances. These suggestions can be aimed at creating an addiction to trance itself, but are more usually intended to generate an addiction for the individual hypnotist. Because this serves to amplify the infatuation effect that's fairly strong to start with, these suggestions can be very powerful. I consider this a highly unethical practice, particularly when used with novice trancers, and one that can have serious first-life repercussions.Protecting yourself
The only sure way to avoid these various dangers is by not exposing yourself to them - in other words, to avoid trancing at all. If you have an addictive personality or suffer from depression it probably would be advisable to avoid recreational trancing. If you don't fall into one of those groups and want to experience trance, the most important thing is to make sure that your potential hypnotist is worthy of your trust. There's no infallible way to do that, but at a minimum you should get to know them before you let them trance you, and ideally you should discuss the issues raised in this article with them. For example, assume that you talk with a potential hypnotist about "addiction" suggestions before trance, and they promise not to use them. If, during trance, they do attempt to insert that sort of suggestion, then their clear breach of promise is likely to be enough to both wake you from trance, and legitimately destroy any trust that you might have had in them.Of course, the idea of addiction can be very seductive in itself. However, consider that if a hypnotist uses this sort of suggestion with you, they likely use it with many others too. Behind every SL avatar is a real person, who has only a limited amount of time they can spend in SL each day. The act of trancing someone can involve a lot of mental energy so a hypnotist is unlikely to want to spend all their time in SL performing trances. Allowing yourself to become addicted to someone who has to share their limited time with many other addicts is a recipe for unhappiness. If the idea of being enthralled to someone in SL is that appealing, it's far better to find someone who you want to be with anyway, and have them learn some basic hypnosis techniques. Hypnosis is not hard to do, and there are plenty of resources on the net to help learn how to do it. Learning to trance as your dom/domme learns to hypnotize is a great way to strengthen the relationship.