...certain shihan that when they enter the room I actually feel a bit sick to my stomach. Others, that when they enter the room it almost feels like a sigh of relief - or some sort of unberdening experience. Maybe it's all in my head/guts.
You're obviously picking up on something, not sure what exactly. Perhaps it's the experiences you've had with them on the mat, being reinforced by seeing them?
But whatever's going on it's causing you an emotional reaction.
Not in aikido, but there have been a few rare times where I've felt someone's "presence." Good and bad. It can be quite disconcerting for me, because I get an emotional response, seemingly from nowhere.
Sometimes on the bus, especially towards the end of summer, I feel a very tense vibe, as if everyone is hot and cranky and barely containing their rage.