To be honest it sounds as though you simply experienced a cannabis 'high' rather than actually 'greening out'! Many people who experiment with any drug, but particularly cannabis, are not completely prepared for the experience and when the drug starts to have an effect it is not as they expected. They then try to fight the feeling and this results in anxiety and panic. That's what this sounds like ... This is why so many people try cannabis once, find out that it doesn't agree with them and choose to never use it again.
'Greening out' (also known as 'whiting out') is often described as a 'cannabis overdose' and is a term used to describe a situation where a person feels sick after smoking cannabis. They go pale (turning 'green' or 'white') and start to sweat; they feel dizzy and nauseous, and may even start vomiting. The experience can be quite frightening and users can become very anxious and start to panic. In extreme cases, the person may experience prolonged vomiting and even hallucinations. Cannabis users often report that the only way they can alleviate these symptoms is to lie down.
Greening out is much more likely to occur if the user has been drinking alcohol before they start smoking. Research evidence shows that because there is alcohol in the bloodstream, the THC (the part of cannabis that gets you stoned) is absorbed much faster. This can result in a much stronger and often far more unpleasant effect than usual. First-time cannabis users can often report similar experiences, although not quite so extreme (but still feeling very unpleasant nevertheless) - they just weren't prepared for the effects of the drug.
This can be a traumatic experience, whether you were on your own or if it happened at a party or gathering with other people around, and it can take some time for a person to recover. Have you 'destroyed' your brain or caused some permanent damage as a result of this 'one-time' experimentation? That is highly unlikely. As I said in a previous posting 'Can smoking weed once have a lasting effect?' - you would have to be incredibly unlucky for this to happen as it appears to be regular use that causes the greatest problems. That said, a one-time use can lead to a terrifying experience, usually associated with anxiety or a panic attack, and it may be something you never forget!