Constant

Mina Bjork explained that when a human telepath/time traveller projects their consciousness into another time period, they need a constant to latch on to that is present in both time periods to help maintain the connection between body and mind. A constant can be any object or person that exists in both time periods that the traveller deeply cares about and could recognize. If a constant is not found, the connection between body and mind is weakened and the individual risks slipping into insanity or losing the connection altogether (thus making it impossible for the mind to return to the body after the projection is complete). It is currently unknown if this rule is unique to humans or if it also applies to other species.

History
When Mina Bjork projected her consciousness into the Dreamscape of every time period in an attempt to find Niflheim, she used Nif as her constant to maintain the connection between her mind and her body.