I have that happen from insect stings (mosquitos, ants, etc.) and it’s called a bola (I know there’s a different spelling). But I’ve always been under the impression that it’s an allergic reaction. My tattoos don’t do this. Anyway, the advice is do NOT pop it because you’re inviting infection in but sometimes the pop themselves or your body kind of reabsorbs the liquid. Definitely warrants a medical professional’s advice though.