Night frights are very common in tiels, not so much in other species I have read. It is in fact what brought me to bird boards a few years ago. Angel had lost ALL flight feathers on both sides and went from fully flighted to falling like a brick. I had NO idea and thought it some rare fast disease. I had stupidly put a small play gym on the floor of the cage thinking that would give her enjoyment playing on. She fell on and into it, thrashing around and also had abrasions under both wings.
With night frights some covered birds prefer to be uncovered, others,the opposite applies. Adding a night light seems also to help tremendously as when dazed after the fright they can see around them. Eliminating shadows (eg if near a window move further away.) as much as possible helps too.
Angel (and the others) are now never covered, have a night light and when I am coming to the kitchen in the night I softly tell them it is me. The frights she used to have have decreased dramatically in number and intensity. Now she (and it also sets the others off) just falls from her perch sqarking, looks around, shakes off the brain fog a bit as she can see where she is and climbs back up to roost. If I am there for a fright I do not touch her I just talk calmly as she orientates herself and settles.