Insight Comes from Dukkha, Not from Bliss - Ajahn Dhammasiha
In our formal meditation, we may experience rapture and bliss of samādhi. But at other times, we may feel no happiness at all, but struggle with an unruly mind, challenging emotions, and a lot of internal pain.
However, there is nothing 'wrong' with us, or with our mediation, if defilements and suffering arise. The important point is to be aware of it, to investigate that dukkha with mindfulness and wisdom, to find it's underlying deep causes, and then to let go of the cause, which will end the dukkha as well.
Therefore, pain, suffering and challenges in our meditation can ultimately be even more beneficial for our progress than bliss, if only we do not shirk away from the tough task to fully face them with awareness and thoroughly investigate them with withdom.