Why is my budgie thrashing in his cage?

Last night my male budgerigar was thrashing around in his cage; it happened three times over the span of a few hours. Each time I got up to see what was going on, I couldn't find anything that might be bothering or frightening him. He didn't even look scared (and I know what a scared parakeet looks like), I just put him back on his perch and then he fluffed up and went to sleep. I know night thrashing is usually because they're startled, but I was wondering if it could be because his companion budgie died recently. This would be an odd reaction to such a thing, yes, but is it possible? If not, what else could be causing this?
Asked Jun 01, 2015

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