What Is Metaphysical Poetry And How Is John Donne A Metaphysical Poet?

The roots of metaphysical poetry are basically found in the seventeenth century, when a group of poets, co-incidentally shared some common features of metaphysical wit. The term Metaphysical poetry was used for the first time by Samuel Johnson in his book "Life of Cowley".
The reason for calling these poets as metaphysical poets is the use of wit and far fetched imagery. They yoke together two entirely opposite ideas together and that too with a lot of conviction and authority.
As far as John Donne is concerned, he is probably the most famous of all the metaphysical poets. John Dryden says about John Donne, "He affects the metaphysics, not only in his satires, but in his amorous verses, where nature only should reign; and perplexes the minds of the fair sex with nice speculations of philosophy, when he should engage their hearts, and entertain them with the softnesses of love."
The imagery used by John Donne is his various poems comprises of far-fetched images. For example, in his poem "Good Morrow", he compares himself and his beloved with seven sleepers. Apparently, both, the Seven Sleepers and the poet and his beloved do not have any resemblance with each other and one might not be able to comprehend the relationship at the first glance. But this is mastery of John Donne that he yokes together such an alien phenomenon with love.
Similarly, Love and Mathematics do not have any relationship at an apparent level. But he compares himself and his beloved with two legs of a compass in his poem "Valediction: Forbidding Mourning".

The term Metaphysical poetry relates to a group of poets of Seventeenth century. This term was used for the first time by Samuel Johnson is his book "Life of Cowley". Metaphysical is generally a term used for things which do not have any physical existence or they are beyond physical existence. For example, ghosts, spirits and even God is sometimes referred to Metaphysics by some philosophers.
On the other hand, when we talk about poetry in terms of Metaphysical, we do not mean that this poetry is concerned with supernatural elements or with the things beyond physical existence. By Metaphysical Poetry, we mean a poetry in which the most heterogeneous ideas are yoked together; the ideas, which apparently do not have any kind of relationship with each other. For example, in general, we may not have any connection between conjugal love and the Seven Sleepers but John Donne makes a connection between the two in his poem "Good Morrow". Similarly, Mathematical instruments like compass and Conjugal love can be the most heterogeneous ideas present on the face of Earth. But both of them are yoked together by John Donne in his poem "A Valediction: Forbidding Mourning".
So, we can say that the Metaphysical Poetry is nothing but a blending of the most distinguished ideas in a beautiful and convincing manner.

The flea and what john donne uses in it as metaphysical' features?