Dhruti means that which upholds or sustains life. For many people, the mind goes hay wire. They cannot even sustain or tolerate a small insult. A little bit of imperfection they cannot tolerate.

Sattvic dhruti is that which sustains the mind, life energy, and activities of the senses. 

That which helps you to be steadfast in your yoga. Not like one day you do yoga and next you go for bhoga (sensory pleasure). Not like that. That which upholds your senses, your life is sattvic dhruti.

Rajasic dhruti is of the type when I get results then I will deliver.

This sort of mindset where your enthusiasm is related to some little reward is rajasic dhruti. It could be related to Dharma or it may not be related. Any work that is taken with the intention of getting results, such as fasting to achieve some results. What is God going to get if you fast?

Tamasic dhruti is one who sleeps a lot.

That is most important for them. Nothing else. Very fearful. You look at their face, they are always down, depressed. If you cannot get married, you are upset. You get married, you are upset. Always regretful. That should not have happened. I should have had like that. After 40 years of marriage, they think they should have married someone else. And arrogance. And one is unable to get of this negativity in the mind. Some people try to get out of it, but they are not able to get out of it. Lazy people, who can sleep anywhere, any time.

One who is lazy, gets scared easily. Then behind fear, comes negative thoughts such as who will cremate me when I die, who will take care of me when I grow old. Some one will complete the cremation rights. Man is mad. If you do not want to leave the madness, then be mad for that which has made all these things not for the things made by Him. Then after this comes vishaad: they think about what happened many years ago and get upset. People will reach Mumbai from Bangalore, and then they will continue to say we should have booked another ticket. Vishaad has become a habit. A person who is enthusiastic and happy, they will not go into vishaad.

How do you get out of Tamasic dhruti? 

Do seva, sadhana, satsang. Tamas gets converted to Rajasic and then to Sattva.