Fresh dandelion greens

So a few minutes ago, I ate fresh dandelion greens from one whole plant, four inches tall, and the flower tops, bunched in the green sphere, didn't eat the stems. Less than five minutes later, there was a very obvious pressure at the base of my skull. Not pain, but sort of concerning, I've got many years of foraging under my belt, but this is a new feeling. Anybody have any thoughts? Thanks.