Hello, nice nice pictures. I admire your presence of mind in capturing the picture of the Lion fish. I am not an experienced diver and have no idea how it feels to be stung by any venomous critter. I do know a thing or two about treatment though.
The mechanics of venomous injuries are the same. Twofold. Initial mechanical injury introduces subdermally by teeth, beaks, barbs, fangs/stinger/spines etc. The larger the size of the break in skin the higher your risk of an opportunistic secondary bacterial infection for example tetanus. Lion fish are quite known for this and you should consider an antitetanous shot not so much for this incident but for the next. Another example would be the Komodo, with its deadly bacterial brew in its saliva, it causes a rip roaring wound infection. Brittle spines that get embedded and breakoff would theoretically increase this risk also. Though not unknown, I have only read about stingers that causes immediate death due to the location of the strike e.g croc hunter.
The second and probably more important effect would be the antigenic nature of the venom. Its well known that most snake bites and stings thankfully do not impart venom, however if it does, venom derrived from a pot puree of proteins are all highly antigenic, (basic training calls for hot water immersion of the part affected in effect to denature some of these proteins without denaturing your hand) our immune system tends to over react to the presence of this foreign protein by numerous cascades of immune reactions most causing the release of various substances that causes colateral damage to tissue, initially seen as redness, warmth, swelling, pain and immobility, the classical signs if inflammation (as opposed to infection). The initial reaction could rarely be systemic (involving multi systems) severe enough to cause fairly sudden anaphylaxis towards hypersensitive individuals, e.g, cardiovascular collapse, airway obstruction leading to death. Its a good thing most reactions tend to be local.
The toxigenic nature of venom is however more well known, i.e venom causing direct necrotising (tissue death), neurogenic (nerve paralysis) and what have you and its consequences.
Coming around to the picture of your left hand, whats apparent is the darkening and creasing/wrinkling of your skin where the alleged sting took place. The darkening is due to recent past collateral damage, blood cells being destroyed and the way our body deals with blood residue, haemosiderin. The wrinkling suggest the inflammatory period is over and swelling is subsiding. I can't make out a physical puncture and also the absence of bleeding which would probably rule out a spine attack. I would however state that your wound would be more that a few days old and that it could be that the puncture had healed. All in all, I am thinking jellyfish.
