Patañjali Yoga Sūtrāḥ 1.6|| प्रमाण-विपर्यय-विकल्प-निद्रा-स्मृतयः ||पतञ्जलि योग सूत्राः १.६|| pramāṇa viparyaya vikalpa nidrā smṛtayaḥ ||

The five categories of thoughts could be: right perception, erroneous perception, fantasy, sleep and memory.

Patañjali Maharṣi says, whatever might be the nature of thoughts — good or bad, they are ripples any way on the surface of the mind (pond), obliterating our inner vision.

Good or bad, negative or positive, vice or virtue, thought is a thought, or a fluctuation, capable of disturbing sādhaka, deviating from the inner poise. Not just the budding sādhakas, even realized yogis might be blown away if they are not wary of these five kinds of thought waves and Bhagavān says:

आरुरुक्षोर्मुनेर्योगं कर्म कारणमुच्यते।

योगारूढस्य तस्यैव शमः कारणमुच्यते॥गीता ६.३॥

ārurukṣormuneryogaṁ karma kāraṇamucyate.

yogārūḍhasya tasyaiva śamaḥ kāraṇamucyate|| Gītā 6.3||

For sādhakas, desirous of Yogic or spiritual progress, (being free from all kinds of dithering thought waves) indifference or detachment is the only way. And for the one who has already reached, stillness or equanimity or poise, control of senses (śamaḥ) is the only effective means (to stay in there, else, he might fall).

In the above verse, Bhagavān distinguishes two kinds of sādhakas: ārurukṣu and ārūḍha. ārurukṣu is a true seeker, desirous of reaching newer and newer heights in yogasādhana. ārūḍha is one who has already reached the summit of yoga. Both are equally vulnerable to fall unless they are wary of disturbing thought waves and wild senses.

Great sādhaka, viśvāmitra falls prey to his own uncontrolled desires (on his surrender to Menaka — an angel of Devaloka). Whereas, Naciketa comes victorious on having not yielded to the seemingly colorful assurances of Yamadharma (kaṭhopaniṣad). A true yogasādhaka feels complete and full only when Paramātma is realised. No other opulence gives him such a fullness.