Former Partridge Family singer and actor David Cassidy has said he is suffering from dementia. The revelation comes after performances in California in which he forgot his words and appeared physically unstable. The 66-year-old star, a teen idol in the 1970s with hits like How Can I Be Sure?, has told People magazine that he will stop touring as a musician to focus on his health. "I was in denial, but a part of me always knew this was coming," he said. Feb.21 http://www.bbc.com/news/entertainment-arts-39035720
Mental health in astrology can be attributed to many different combinations of planetary aspects, house rulerships and so on. The relationship between the 3rd house and mental health, for example depression or dementia, doesn’t seem to be as common knowledge as some of the other astrological influences. In David Cassidy’s chart  we notice that a Mars-Uranus conjunction is taking place on his radix Sun which is the ruler of his 3rd house. The Sun is conjunct the asteroid Psyche (mental health) and opposite Neptune (confusion, disintegration) so that the Uranus transit reinforced by the Mars conjunction is bringing about dementia for the singer.
This is the astrology if we limit ourselves only to the planets and asteroids. However, if we now turn to the stars that form the backdrop to Cassidy’s radix Sun, the images offer a greater depth to our analysis. Here we have stars in the belly of Cetus, the sea monster and some others in the head of King Cepheus. The sea is linked to the unconscious and the sea monster is symbolically the chaos that the unconscious can produce when it destabilizes the conscious mind (Cepheus’ head).
In mundane astrology we can draw charts for the exact aspects that Mars makes with Uranus, Jupiter and Pluto as it triggers the T-square. If any one of these charts carry the T-square in aspect to the horizon or meridian, those places will feel its full effect. Shown here is the chart for Mars opposite Jupiter drawn for Agoura, CA where Cassidy was performing last weekend when the incident reported occurred. Notice that the Mars-Uranus-Jupiter-Pluto T-square is anchored to the horizon axis. Since Mars-Uranus conjoin Cassidy’s radix Sun [22ar] this becomes one place where his mental issues become manifest.
Finally, we notice that transit Sun is conjunct the South Node on the Ascendant. This is a phenomena known as “Moon Wobble” which research has shown to be linked to mental instability.
Moon Wobbles were discovered in the 1930's, when research by astrologer Carl Payne Tobey (1902-1980), the original editor of Astrology Magazine, revealed that disasters occur in cycles associated with the conjunction (0°), opposition (180°) and square (90°) from the Sun to the Moon's Node. These powerful contacts occur when the Sun and the Node are in the same sign, or the opposing sign, or when the Sun is in a square aspect to the nodal axis.
During Moon Wobble the instability factor is high, resulting in more accidents, fires, plane crashes, freak accidents, floods, feats of nature, bizarre weather patterns, earthquakes, tornadoes, violence, Terrorism, riots, and political and personal upheavals. These Cycles bring suppressed energies in people and Mother Nature to the surface, erupting and disrupting. Remember, if you are not working through your subconscious issues you are more likely to fall prey to your emotions. .