Patanjali Yoga Sutra — वृत्तयः पञ्चतय्यः क्लिष्टाऽक्लिष्टाः||१.५|| — vr̥ttayaḥ pañcatayyaḥ kliṣṭā’kliṣṭāḥ॥1.5॥
Thought waves could be any of the five categories. Some are troubling or disturbing and some are not.
Patañjali Maharṣi classifies five kinds of thought waves haunting the mind. Some could be painful, whereas some are not. Some thought waves, apparently pleasurable, could be painful in due course. Some seemingly painful could be blissful in the long run. A thief momentarily feels very happy with the valuables he has stolen. But, slowly he starts fearing the threat of arrest. His life turns miserable, though he is in possession of the stolen treasure and though he is not arrested by the police yet. If arrested, real hell. Even if not arrested, his conscience would prick him or the fear of arrest never allows being at peace. In Mahābhārata, śrī Kr̥ṣṇa says, whether one follows dharma or not, definitely one knows what dharma is. If not the conscience, fear of arrest would make him miserable. Either way, he is not happy. Another example to prove the other way round: All efforts of spiritual Sādhakas appear to be very arduous initially. But the bliss is unmatched when they realize the Lord, pinnacle of spirituality (Prahlāda, Nachiketa, Dhruva, etc). Is there a better bliss than yogasādhana and realization of that summit of yoga? The end result is the litmus test. You are what you think. You are what you do. You own the full responsibility for what you have chosen to think or do or speak. The only index that tells you what you are is your mind.
Srī Kr̥ṣṇa wonderfully declares as under:
यत्तदग्रे विषमिव परिणामेऽमृतोपमम्।
तत्सुखं सात्त्विकं प्रोक्तमात्मबुद्धिप्रसादजम्॥भगवद् गीता १८.३७॥
Initially, it appears to be poison (discomforting) in the beginning but leads one to the nectar of supreme bliss. That kind of happiness is called sāttivik.
विषयेन्द्रियसंयोगाद्यत्तदग्रेऽमृतोपमम्।
परिणामे विषमिव तत्सुखं राजसं स्मृतम्॥भगवद् गीता १८.३८॥
The happiness that springs from the union of sensory objects and senses appears to be nectar in the beginning but leads one to the fatal poison. That kind of happiness is called rājasic.
