Hello!
I read your question and I wanted to answer because I identify a lot with her, since I am one of those people who can not sleep if they do not take a shower before !!
Answering your question, nothing really happens if you do not shower before going to bed, that's optional, in fact there are people who only shower once a day, in the morning before leaving their homes and sleep peacefully, Everything depends on the daily routine you take and how you feel.
Personally I feel uncomfortable without showering, I feel dirty, sweaty and I feel that the shower is necessary to relax.
If you want to shower or not at night before going to bed is your decision but I can leave some of the advantages or disadvantages that showering at night to convince you to do!
By not showering at night you can produce acne in various parts of your body because the sweat and fat that occur during the day stay in your body so when you shower before going to bed you would be eliminating all that and avoid the acne.
If you suffer from allergies I recommend that you shower at night because when you do not shower you produce dirt and dust that clings to your sheets, and I for example am allergic to dust and not showering would give me an allergy.
When you shower at night you relax, if you had a hard day at work or if you had a hard day at the university or a hard day in general and you shower at night with hot or warm water your body relaxes and you can rest your mind of so many problems, and that your muscles relax when you feel the hot water and you enjoy your shower so the time to sleep, you can sleep rested and with less stress and in fact the next morning you will feel that you slept more hours since you relieved all the tension and stress accumulated with the night shower.
In general we can say that after a shower, we are all invaded by a sense of well-being, we leave feeling deep hygiene, and there is nothing more pleasant than putting on some comfortable clothes, and laying on a mattress to rest.
Then nothing really happens to you if you do not shower at night, but I can assure you that it has many positive effects, by doing it you will sleep better, you will surely feel the difference so I recommend it 100%
Goodnight !!