This phrase, "Let go and be happy" sounds simple, right? No. I know it's not. There are many samskaras (impressions from life experiences) blocking our ability to allow life's events to pass through us freely. The blocked energy is stuck and has now created a problem when we experience a similar event that "triggers" the energy pattern. This is why you can actually feel the fears and insecurities of a five-year-old when you're sixty. What is happening is that unfinished mental and emotional energy patterns are getting stored and reactivated. When these feelings come back up, we have a choice to open and relax our heart, forgive, laugh or do anything to feel and let it go. Just don't push it back down again. As you continue practicing "letting go" it will get easier and you will become accustomed to the process of releasing and cleansing.
Your center of consciousness is always stronger than the energy that is pulling on it. As we learn to remain centered with smaller things, we can see that we can also remain centered with bigger things. Life creates situations that push us to our edges. Fear is caused by blockages in the flow of our energy. When our energy is blocked, it can't come up and feed the heart. It is stuck in the lower chakras. The process of letting go the moment it hits is spiritual growth. No matter what events take place in life, it is always better to let go than to close.
Meditation creates many opportunities for us to work through our samskaras. When we are quiet we can observe our thoughts. We realize we are not our thoughts. We can stay in our comfort zone and the cage we have created around us to keep us "safe." Or we can work on our freedom and expand. We will have mental disturbances. But they do not have to cage us in. We let go and choose instead to be happy.
"Events don't determine whether or not you're going to be happy. They're just events. You determine whether or not you're going to be happy. You can be happy just to be alive. You can be happy having all these things happen to you, and then be happy to die. If you can live this way, your heart will be so open and your Spirit will be so free, that you will soar up to the heavens." You don't have to be outwardly glowing all the time, you're just joyful inside. Instead of complaining, you're just having fun with the different situations that unfold. This is unconditional happiness.
Source: The Untethered Soul: the journey beyond yourself by Michael Singer