Yep -- Tom's behaviour so shortly after he poured out his heart to Neelix (Parturition) and Janeway (Threshold), and when he's still doing stuff like being kind to Doc, is kind of odd, isn't it ... The reasons for why he caught that bug that seems to be plaguing him will be obvious in the next ep.
And while you are watching the next one ("Investigations") look for the cameo of a Very Famous Person early on, handing Harry a PADD in a corridor. And if your mind tells you "nooooo -- it can't be ... But he's a ..." rest assured: it IS who you think it is.