Ketu which is known to be the planet of liberation(Moksha) is the most spiritual planet of all. In the initial period of Ketu Mahadasha it can cause great havoc in the material world . Ketu provides his harsh way in teaching lessons during its Period and makes the native more inclined towards occult realms, things beyond common understanding.Ketu is the planet which provides nirvana to the soul.
After coming out from Mercury Mahadasha you may feel that you are intellectually brilliant and infallible. Once you enter Ketu Mahadasha all the ego that got developed will be corrected quickly by unwanted fears, confusion, stomach issues , headache , sleepiness, tiredness , thyroid problems or even diabetes. One should be careful of thefts, poisons, weapons, fire and water elements. Friends may backstab you which can affect your reputation in the society.
This planet may detach you from your family, friends, children, job depending upon its placement along with other planetory alignments.
During its Period you should channelize your energy and time towards philosophical subjects, virtuous pursuits, worshipping, and practicing Ayurveda. Interest in Yoga and meditation increase during this period. Some religious travels and pilgrimages are also possible during this Dasha.
Few examples of what can be seen during Ketu mahadasha is people start learning a lot of shlokas ,hymns, and Mantras, some people get into a situation where their family member becomes very spiritual and they get influenced by the same , there are also some situations where people go through some kind of traumatic experience and spirituality or yoga helps them to get rid of it and they continue to be ritualistic/religious bend of mind.
If Ketu is a yoga karaka or Yogi the negative effects will be much reduced, so much one will not notice that he or she is going through a Ketu dasha.
The person born in Aswini, Magha and Moola stars will start their life with Ketu Maha Dasa.
Ketu Mahadasha will never come to your life if you are born in these Nakshatras - Bharani, Poorvaphalguni, Poorvashada
One who born in the star of Aslesha, Jyeshta and Revati, will go through Ketu dasha in teens or early 20s. hence they need to be careful because this is the time when karma starts to manifest itself. This is the time to study in college, may fall in love or may get some job or may get involved into drug addiction, alcohol etc. Thus parents need to be more careful .
Ketu do well if it comes under the influence of Jupiter and Venus, who are the gurus of Gods and demons respectively.