What happened to you is extremely unusual, and I suspect it has nothing to do with vaping.
Regardless, 8mg is considered really low, and most people start with much higher strengths than that.
But it's hard to give any advice when we don't know...
--How much you used to smoke
--How many milliliters of 8mg you vaped
I disagree a bit. The same thing happened the first week when I switched over. I was vaping 18mg - 70/30 pg/vg... Those first few days I got buzzed, light headache, feeling restless, heart pound. I'm assuming just the effects of taking in the nicotine differently. It soon passed...I just cut back my nic in my juice to 12mg...which allowed me to still feel like I was "smoking" so I didn't revert back to analogs. I drank a lot of water.
After a week or so this all went away... Now I vape 18mg all day long...without so much as a symptom (if you want to call it that).
I think its normal and nothing to be worried about. However, if the OP does...of feels its something outside the norm...then they should consult their physician and not post on a board about it.