Patañjali's yogasūtras 1:5-6

As we go forward, it helps to note that the yogasūtras were not written  as a teaching tool. Concepts are not explained in order, starting from the simple, going to the complex. Rather they presuppose a knowledge of the entire system. Scholars believe that they were a way of preserving the expert tradition. That makes it harder for us to understand the sūtras, and the interconnecting concepts, till we have read about them all*. But having studied them for a year, I believe the effort was more than worth it. 

{1:5}
वृत्तयः पञ्चतय्यः क्लिष्टाक्लिष्टाः 

वृत्तयः पञ्चतय्यः क्लिष्टाः अल्किष्टाः 

Modifications [of the mind are] five-fold [and are] painful [or] non-painful

वृत्तयः - nominative plural of वृत्ति - activity, modification

पञ्चतय्यः - five-fold agreeing with वृत्तयः

क्लिष्टाः - tormented, injured, pained - adjective agreeing with वृत्तयः from √kliś (9P) to torment, to afflict 

अल्किष्टाः - not connected with pain or suffering

Importantly, the vrittis (activities of the mind) are classifed as kliśṭa and 

akliśṭa, because of their connection to a central yogic concept - that of 

kleśas (suffering, affliction) which are treated in Ch 2, sūtras 2-12. 

At one level this  sūtras refers to simple experiences - a beautiful sunset, freshly cut grass, road-kill, the living dead; or even neutral experiences - stirring tea, combing one's hair. Interestingly what is pleasurable for one person, may not be so for another. Not everyone loves the opera, blue cheese and wasabi. There are people who don't like dogs or are downright scared of them. The reason for these individual reactions is treated later in the sūtras. But it bears reflection at this stage.

{1:6}

प्रमाणविपर्ययविकल्पनिद्रास्मृतयः 

प्रमाण विपर्यय विकल्प निद्रा स्मृतयः

[These are] right knowledge, wrong knowledge, fancy/imagination, sleep and memory

प्रमाण - right perception (sing., neuter., nominative)

विपर्यय - misapprehension, error (sing., masc., nominative)

विकल्प - contrivance, imagination (sing., masc, nom)

निद्रा - sleep (sing., fem., nom)

स्मृतयः - स्मृति remembrance, memory from √smṛ (the plural ending is because all five states are in a compound ending with  स्मृति)

Pramāṇa and viparyaya comprise of all those activities in the mind which are formed by direct contact through one of the sense organs. Vikalpa, and smṛti are internal processes produced in the mind without any contact with the outer world. Notice that in our waking state, we can control Vikalpa (imagination), but in the dream state we have no control on it. These states, including nidrā are explained in detail in the next five sūtras.

*If you can, please read about Sāṃkyha and Yoga in  M. Hiriyanna's excellent and affordable book "Essentials of Indian Philosophy" http://www.amazon.co.uk/s/ref=nb_sb_noss?url=search-alias=aps&field-keywords=m+hiriyanna