This post is primarily for people who have chosen to do HRT (Hormone Replacement Therapy.) Your emotions might fluctuate during transition if you aren't on HRT, just because of your choice to come to an authentic expression of yourself. But hormones are really powerful, and can have large effects on our emotional lives.
Emotional changes due to HRT can be unpredictable in when they can occur (that is, how long after you start HRT), how strongly they occur, and how they feel to you. If your starting at a low dose, they might be quite subtle. And there can be effects that are more clearly connected to the hormones, and others that are less obviously connected. They can be somewhat different for trans men than trans women, although there are some things in common, including mood swings, and euphoria.
Not everyone experiences euphoria, but many trans people feel euphoria in the presence of the "right" hormone - the hormone that reflects their gender. Trans men often find that anger and rage come more easily, and crying is more difficult, and trans women often find the reverse, but this is not at all universal.
Emotional Roller Coaster
HRT, especially in the first year, can be an emotional roller coaster ride. How best to deal with this?
First, remember to be compassionate with yourself. Remember this is part of the process of transition, and you are OK, and valid as you are, no matter what you are feeling. Practice just being with your emotions, and not acting out of them. Notice where your emotions are showing up in your body. Just let yourself feel the sensations of the body.
Emotions are short-lived in the brain. If you let yourself really feel them, focus on the body, and not the thoughts arising, they will fade pretty quickly. If you feel overwhelmed by these emotions, or they have activated past traumas or mental health issues, finding a therapist or mental health professional to work with is highly recommended.
A Chance to Befriend your Emotions
None of your emotions are bad, even if they can be uncomfortable. Sadness, fear and anger, in particular are uncomfortable emotions, but they aren't bad, they just are. Give yourself compassion if you find yourself feeling bad about feeling those emotions. It's natural to want them to go away.
This transition process is actually a chance for you to get to know your emotions a lot better, and befriend them. As you are willing to experience your emotions in your body, give yourself compassion for them, and pause before acting out of your emotions, you can allow them to be present in you, and experience them without feeling like they are a problem, because they are not a problem. Your emotions are never a problem, unless you make them a problem (which is something that we do very often by habit.)