The problem with the theremin when it comes to nerves, is that unlike other instruments the theremin is transparent.
If you're jittery for a piano recital, as long as you're well rehearsed and reasonably concentrated, the mechanism of the piano will hide your jitters. This is true of most other instruments as well. As long as there is some sort of mechanical action between you and the sound, you're safe.
With the theremin, the actual interface is invisible. In every real sense the thereminist IS the instrument. He/she is controlling every aspect of the sound at every instant, which is not true of many instruments. Once you have struck the string of a piano, a guitar or a harp, the deed is done and the instrument will take care of the rest. A thereminist, on the other hand, is involved with every aspect of the sound of a note from the instant it is heard. The most subtle nuance of intonation, vibrato, and volume must be controlled with absolute precision and the instrument, through its sound, will reflect even the slightest involuntary motion on the part of the player.
The "snowball effect" is something that plagues thereminists. This is a self-perpetuating and steadily worsening phenomenon that can be initiated by the slightest mistake. You play a note that is noticeably off key and are so disconcerted by it that the general level of your performance immediately begins to fall. Your anger and disappointment at yourself for having been unable to play the way you wanted become the triggers for more errors which, bring on more anger and disappointment, resulting in a significant "snowballing" loss of control.
This is one of the reasons why theremin performances are usually better at the beginning of the program than at the end.
The theremin is an instrument ideally suited for the recording studio, where all aspects of the environment can be controlled.
"Technology has the capability to create a climate of anonymity and to allow the artist the time and the freedom to prepare his conception of a work to the best of his ability. It has the capability of replacing those awful and degrading and humanly damaging uncertainties which the concert brings with it." Glenn Gould