Public speaking is often cited as people's number one fear. Most people probably don't consider public singing. But if they did, I bet they'd think public speaking was a breeze.
It's likely not really true that public speaking is the number one phobia, but it is still a serious fear for many, many people. It's what's known as a social phobia, and seems to be prevalent in some form or another in the general population. In other words, fear of doing hard things in public is very, very common.
A social phobia is defined as a fear of being watched or judged by others. When it becomes intense or disruptive to a person's life, it can be elevated to social anxiety disorder. It is more than feeling shy or introverted when put into public spaces, but rather it is the thoughts about what others might be thinking that lead to physical symptoms, avoidance of the situations where this might occur, and disruption in a person's daily life. It also cannot be waved away by telling someone just to get over it or think happy thoughts.
Performance anxiety is so common that we've got books and myriad articles written on the topic to help singers try to understand it and overcome it. The process for dealing with performance anxiety can be so complex, because how people experience it can depend on their unique past experiences, their current unique circumstances, and their unique views of themselves and their abilities. That's a lot of uniqueness to manage! There are some things that we can pursue in the studio, however, to try to give our clients the tools to manage the anxiety.
First, acknowledge that it exists and your singers are not weird. Tell your own stories of feeling nervous before a performance, and how you have personally learned to deal with it. I'd also caution against sugar-coating it entirely. Be honest about when things worked out fine, but also when things didn't. While we want to reassure our clients that everything will be fine, the truth is sometimes it won't. Sometimes our nerves can sidetrack things. BUT! We all made it through and we're still singing. It can be important to remind folks that there is life after a big mess up.
Second, try some role playing. See if you can set up a rehearsal in the space where the performance will be. I think ideally this should happen several weeks ahead of the performance, rather than just a few days or the day of. I say this because after the rehearsal, you can practice visualizing the space several more times before the performance, and that gives the mind time to think through how it could go and acclimate itself to the memory of how the rehearsal went. This may be a pie in the sky kind of scenario, but you could try it a few times to see how it works for you. (There are also several neurological reasons to rehearse in the space as much as possible.)
Third, try a book club with your clients to be proactive about addressing performance anxiety. One book that has been very popular among singers is A Soprano on Her Head by Eloise Ristad. You might also consider hosting a master class of sorts, with a therapist who specializes in anxiety coming to talk about coping strategies and answering questions of your singers. Sometimes just acknowledging that we're not alone in our feelings can be really helpful in finding help.
Performance anxiety in singers is normal, but it doesn't have to be debilitating. I hope that if you experience nervousness before singing that you seek out help so that you can still sing with confidence, wherever your performance happens to be. The world needs to hear your voice!
Furmark T, Tillfors M, Everz P, Marteinsdottir I, Gefvert O, Fredrikson M. Social phobia in the general population: prevalence and sociodemographic profile. Soc Psychiatry Psychiatr Epidemiol. 1999 Aug;34(8):416-24. doi: 10.1007/s001270050163. PMID: 10501711.