It is possible to exercise while having FND symptoms.
The key is to establish a baseline then go at your own pace. When you have set your baseline you need to give your body time to settle into the level. How long this takes will vary from person to person but it can take weeks. You will be ready to gradually increase your activities when you feel your body has acclimated to the level and you can confidently sustain it. Like before you had symptoms you can imagine how hard it can be to be consistent. There is likely to be pressure from everyday life or a particularly symptomatic day to deviate from your exercise routine. However, it is imperative that you continue a regimen at any level, even if you have to do less than baseline, in order to maintain a routine.