Yōga Sūtra 1.06

प्रमाणविपर्ययविकल्पनिद्रास्मृतयः।

pramāṇaviparyayavikalpanidrāsmr̥tayaḥ।

[प्रमाण विपर्यय विकल्प निद्रा स्मृतयः।
pramāṇa = activities are validating the evidence; viparyaya = over thinking; vikalpa = imagination; nidrā = sleep; smr̥tayaḥ = recalling past experiences from memory;]

They are: pramāna, viparyaya, vikalpa, nidra, and smritayaha.

When mind takes the form of activity, it can only be in one of the above five stated activities. They can be difficult and not so difficult.