You shouldn’t feel drained after working with a demon, especially with your other symptoms. Its not unusual to experience physical sensations, some are not always comfortable, but drained and the heart thing, dizzy? No. I hate to cry parasite!! But Parasite! 
That happens sometimes when you work with demons, they come in too occasionally, and yea they make you feel like that, or heavy, it’s very strange how they make you feel. King Paimon is wonderful, if anything you may be a little tired afterward, but not the way you described. So next time you call on him, ask him to prevent any astral parasites or other negative entities from affecting you and attempting to attach. Have had similar experience when working with Asmodeus. They will protect you, if you ask.
You don’t need to hear or see him (or even sense him at all) to get really great results.
Also pretty strange to feel drained after a ritual, especially like that… it is possibly the ritual you are doing opened you up to a parasite, in the future I’d really recommend doing a good Banishing Ritual before you do a ritual in the future, and use his sigil.
For a good Banishing Ritual I’d recommend The Sword Banishing in Magickal Protection by Damon Brand, or The Circle of Power from Archangels of Magick by Damon Brand, it’s also in Demons of Magick by Gordon Winterfield.
Was this your first time doing a ritual?
Oh really? A parasite?
No I have done this a few times, I have never felt like that before
It’s possible. Just take note of how you’re feeling for the next few days and see if there’s anything different. If you feel strange then you could try a banishing, that should clear things up.
Could be a sign something else got through. If you’re feeling particularly fearful of anything the next while then that could be another sign. But if you were concentrating really hard then that can be draining of course, so just be wary.
Thank you so much 