Four short lines capture what it feels like when another person's presence stays with you after they've gone. The speaker is overwhelmed by someone they clearly desire: their fingers tremble from the "heat" of this person, and they shudder at a touch that still seems to hang on their skin and in their hair. Even the senses get tangled here, since a touch has a "scent," as if the memory is too strong to stay in one category.
The central image is the sunspot, the bright blotch you see after glancing at something dazzling. It fits well, because the person is like the sun: warm, bright, a little too much to take in. Like a sunspot, the feeling floats around in the speaker's vision and won't fade on command. The mood is intense and a bit dreamy, mixing longing with a slight dizziness. The last line, "long after you're gone," adds a quiet ache. The closeness is over, but its afterglow remains.