I've started to meditate in recent days. After meditation, one day I feel happy and the other day I feel upset, angry and depressed. Also, at the end of the meditation I feel like I just woke up from sleep. Why is this happening to me? Is there any solution to overcome this issue?
Ven. Vijithananda said this is due to practicing Samatha meditation. When you practice Samatha you have the irritation towards any disturbances to your meditation such as sound and the people around you. You also irritated for not being able to experience that meditative happiness. As per Ven. Vijithananda, sleepiness is some sort of progress (defeating four Maras) however you have to go beyond sleepiness. The solution for this is to practice Satipathana.
Are you sure you’re not just noticing your regular mood fluctuations? Meditation makes us more aware of our internal states. Without sitting, we are often oblivious to what’s going on within us. When you start sitting, you begin to notice the good along with all the time you really spend being tired, despondent, and annoyed.
This happens because the meditation lack alertness. You focused on calmness without cultivating vitality. That will surely bring about drowsiness, and it leads to sleepiness.
In this state of non-wakefulness, of non-clarity, discernment is very weak. So, it's easy for any mental obscurations such as anger or sadness to build up without your noticing. So, by the time you 'got up' from the blurry state, your mind is filled with them.
Here's an easy way to prevent this: Meditate with your eyes open.
Meditation link people easily to the spiritual world including underworld as well. This is why lots of people declared that they can “see” the ghost or other beings without physical bodies in spiritual world and at the same time they usually have physical or mental health problems because the ability to “see” is die to them being possessed by the spirit. So it is not recommended for ordinary people to do meditation especially without being guided by a professional around. The safest way to reach enlightenment is by reciting for an example in Guanyincitta Yin Citta Dharma Door the daily homework’s and combined mantras called Little House paying back karmic debts. With the debts reducing for the time being, one will live healthy and happily since the spirit/karmic creditor and the karmic obstacles are the root reason for problems.
It is good that you take note of your mind throughout the day.
When you discern these mindstates you can learn how to they come into being and start to discriminate which states get to direct your behavior, eventually one can attain seclusion from unprofitable states and get deep into meditative composure.
Things you might want to study on this are sutta dealing with; - timely development of factors of enlightenment - denourishment of 5 hindrances - stilling of distracting thought sutta - 36 mental explorations mn140 - honeyball sutta - verbalizations of craving sutta - noble search sutta