Once did my thoughts both ebb flow
As passion did them move
                                    Ananymous          
                 
The metaphor in the first line identifies the speakers thoughts with the tidal flow of a sea or ocean, and then the sacond line expands and fulfills the first metaphor with another, identifying his passion with the moon: his passion moves his thoughts as the moon controls the tides.
The implication is specially interesting in this context because mental disorders were long associated with lunar effects (as can be seen in the common word "lunacy"). The poet seems to be implying, then, that the effect of his passion on his thoughts includes at least a touch of madness.