Yeah. If you had real good stuff 5 to 10 grams is more than enough for someone with little opiate tolerance to feel good. A "heaping tablespoon" could be anywhere from 10 to 20 grams, probably way too much for a newbie to kratom. Use a scale and take smaller doses next time - most people find kratom produces a rather stimulating high unlike most strong "classical" opiates. If I recall correctly many of the alkaloids in kratom have adrenergic effects similar to yohimbine and friends.
You may find slowly sipping tea made with some honey in it allows you to titrate your dose a little better, rather than tossing and washing as I assume you did.