The feeling that we are alienated from our true selves, against God , against each other and against nature.
*sigh*
Given what pantheism actually means - i.e. that there's no difference between Nature and God; that they're synonyms for the same thing - then strictly speaking it's impossible to be alienated from it. That would be like saying you can climb out of the natural world, which is absurd.
On a subjective level you can certainly
feel yourself to be alienated from nature; it often happens in times of deep clinical depression. Coleridge described it well in 'Dejection: An Ode' when he referred to the stars, clouds and moon that normally gave him transports of delight: "I see, not feel, how beautiful they are."
Feeling alienated in these ways are quirks of human psychology. Sometimes they pass on their own without treatment (even the severest of depressions pass over eventually provided you can stand it long enough to wait for it to go), sometimes they require treatment.