The term "snapped attention" generally implies a sudden and intense focus on something. Antonyms (words with opposite meaning) for this phrase would therefore be words that indicate a lack of interest or attention. Some examples of antonyms for "snapped attention" could include: indifference, apathy, boredom, disinterest, inattention, lethargy, neglect, and unconcern. If you wanted to convey the opposite of someone who is completely absorbed in something, you might say they were "distracted," "unfocused," or "uninterested.