While both equity and credit bubble both involve higher price fundamentally, the underlying theses are generally inversed relatively to the implied volatility. This is a thought on the philosophical layer, and as such, in practice, there is some level of linkage in the capital flow between the equity and credit market.
An equity bubble is a bet that the future will be radically different, than the upside from the new venture has no limits. Investors are extrapolating far into the uncertain future, which typically paired with duration, implies highly volatility.
A credit bubble is the inverse, a bet that the future will be like the past. Credit positions only gets more valuable as the consensus view of the future narrows, which typically implies lower volatility.
Intersection notepad 