The original idea for Heliate was generated by  chiefy (http://www.furaffinity.net/view/11422278/) The idea goes that it is a self-replicating helium like substance. Once introduced into your body it has two effects.

1) The first is that it starts converting bodyfat into a lighter-than-air substance that is significantly less dense then body fat and so it expands, though somehow without damaging the host. It will continue to replicate until the body is neutrally buoyant or almost there, though it can also 'bubble' out of them. Also, if more heliate is forced into someone, they will become positively buoyant.

2) It also puts the host in a euphoric state, making them crave physical contact with . . . basically anyone. And because it can be transmitted and is super good at replicating . . . anyone the host touches quickly becomes infected.

Sorry I didn't make that clear in the original post. Like I said though, your character is basically in a euphoric state and happy to have anyone to be in contact with, so she's not exactly thinking clearly.

Thanks for the good explanation