RN here. As previously stated hot water dilates blood vessels, alcohol also dilates blood vessels. When you blood vessels are dilated, your blood pressure falls. When you are seated, this is not a huge issue.
When you stand, you blood pressure can/will fall even more. If you are sufficiently inebriated, the fall in BP plus cerebral depressant effect of alcohol can make you much more prone to passing out. Again moderation is the key and perhaps if going to have a little more than normal, turning down the temp a few degrees.