I don't drink a lot, and previous times I've been drinking I've felt the effects pretty quickly, but the past couple of times I've had a drink I've drunk more than i usually do and I don't feel anything at all. Not even tipsy. Does this mean anything? I don't see how I could have become tolerant of it so quickly, and although I wasn't drinking on an empty stomach I wasn't exactly full.
bathsheba is right. Alcohol is a depressant, and it can subdues the parts of the brain which control judgment and inhibitions ... leading to you feeling "stimulated".
Which is fine if you are in a good temperement already. It will make you feel even more happy, and you may not be conscious that it is having any effect on you. But if you drink when you are not in the right frame of mind, say stressed, then it can really muddle you up.