During his delusionary episode, he firmly believed he could fly.

delusionary 是由名词 delusion（妄想、错觉）加上形容词后缀 -ary 构成的形容词。delusion 来自拉丁语，表示"欺骗、错觉"。delusionary 意思是"妄想的、错觉的"，用来描述与妄想症相关的状态或行为。