I have struggled with sɛҳuąƖ dreams for several years now. I have always purposely purposefully worn looser undergarments for sleeping. However, these naturally allow for more sɛҳuąƖ movements. I have always told myself that I do not want to be scrupulous and my intention is not to force myself to have sɛҳuąƖ movements. But am I still committing a sin if I can just as easily wear slightly tighter undergarments? Or even if I ignore my natural bodily movements and do not have impure thoughts, am I still deliberately causing the sɛҳuąƖ dreams(Which would be a sin according to St. Thomas Aquinas)? Or is this all just scrupulosity? I would ask my priest but I don’t know that I will get a very good answer from the local SSPX priest (I know it wouldn’t hurt to try). furthermore he does not like to talk to people and is hard to catch when he leaves the chapel after Mass.

I have struggled with sɛҳuąƖ dreams for several years now. I have always purposely purposefully worn looser undergarments for sleeping. However, these naturally allow for more sɛҳuąƖ movements. I have always told myself that I do not want to be scrupulous and my intention is not to force myself to have sɛҳuąƖ movements. But am I still committing a sin if I can just as easily wear slightly tighter undergarments? Or even if I ignore my natural bodily movements and do not have impure thoughts, am I still deliberately causing the sɛҳuąƖ dreams(Which would be a sin according to St. Thomas Aquinas)? Or is this all just scrupulosity? I would ask my priest but I don’t know that I will get a very good answer from the local SSPX priest (I know it wouldn’t hurt to try). furthermore he does not like to talk to people and is hard to catch when he leaves the chapel after Mass.

Are you married? I assume you don't watch "that stuff".

It's scrupulous in my opinion. 

First of all, you must pray for purity as one of the prophets in the Old Testament said," As I knew I could not be continent unless God gave it, I prayed to the Lord". You must also practice devotion to Our Lady, the Virgin of virgins. Do the consecration to the Incarnate Wisdom according to the method of St. Louis de Montfort. You should also do fasting and mortification as Jesus said in the Gospel.

Another thing you can do, if you wear a medal, or crucifix; wrap the chain onto your non-dominant hand when you go to bed. Find a way to weave it into your fingers so that it doesn't cause circulation problems, but it can't come off by itself. Hold the crucifix in you hand as long as you're awake and pray and meditate until you fall asleep. If you wake up to any degree, you will notice the chain and remember why it's there. Resume praying until you fall asleep again or get up. If you don't become conscious enough notice the chain, then you're too out of it to be responsible.

It's very important, when awake later, not to think about the dreams that you may have in connection to this. That can likely be a sin.

I suppose you go to confession. You should be asking the priest in the confessional. You have to ignore the thought that the priest is busy or doesn't have time. Consider that the devil's suggestion.

I do not even remember the dreams at all. I simply wake up in the morning and know from deduction that I had them.

Then you’re scrupulous. If you’re a young, healthy male, not engaging in any type of impurity on purpose, put it out of your mind by distracting yourself with other things. It’s a temptation common to young men. Don’t worry about it. Don’t think about it. 

Unless you're subjecting yourself deliberately to various stimuli during the day that would contribute to these dreams, there no sin whatsoever.  If you meditate more on the things of God at all times, they will dissipate and decrease over time, where you might find yourself even in your dreams rejecting temptations against purity.  But even if that doesn't happen, there's no sin.  I find it worse in terms of physical reaction to NOT wear extremely loose clothing.  But people are different.  I can't stand having my feet covered where's my wife likes to be stuck under a tightly fitted sheet.  I would choose clothing primarily based on what you feel comfortable with ... and other circuмstances such as if you have children not wanting to walk out of your room looking obscene in case you need to use the bathroom or get a drink of water, things line that.  But outside of that you're under no strict moral obligation to change how you dress for bed based on their tendency to cause dreams.  As another poster pointed out, you may want to time some workouts to dissipate testosterone levels overnight.  I can't recall the cycles but you can look them up.