When I woke up and looked around, I realized it had all been a dream.

Literal

Eyes [obj-を] awakened-and-looked [discovery-と], everything [subj-が] dream was [nom-こと] [subj-が] was-understood.

一切 (いっさい, 'everything, all') is a slightly formal word. ~ことがわかりました ('realized that') uses こと to nominalize the clause and polite past of わかる. Three discovery layers: waking, looking, realizing.