When it comes to mood swings, I can imagine that anyone with Lyme Disease has had them at one point or another. They seem to be inevitable and the most common one is irritability.
Intentionally demoralizing another person whether it be family, friend or even a complete stranger isn't really in our nature. The simple act is nothing more than an indication of a concealed cause. In our case the cause happens to be Lyme Disease and many times we have to remind ourselves after an episodes that this isn't who we really are. Thoughts of guilt start to set in and you question yourself as to why you couldn't have prevented such an outburst despite your ability to fully understand the cause.
The reason I believe is instincts. It's out of your control when the moment arises and why is that? Well my theory is that human nature is taking over to protect you. You are very ill, weak, exposed and vulnerable so in order to survive, you're unknowingly going to attempt to push back any threat to your well being.
Let's be honest. Your only true purpose in life is to survive. You have a bacterial infection inside of you that had intentions of killing you but your persistence, patience and resistance have disrupted its plans. So you're not dead nor are you really at a level of great health or homeostasis. You're suffering and you've been suffering for so long. This is not a normal stage of life to be in for such an extended period of time and in order for your body to adapt it's going to have to execute an instinct without your approval or knowledge.
As you become more reacquainted with your quintessential nature by force, your natural ability to learn is allowed to take hold. You learn to understand and become more cognitively aware of your irritability and this allows you to control or subdue it. This is a choice based solely on pure will and it takes an exorbitant amount of self control to implement. Remember, you're only human and can only handle so much before a line is drawn.