Below is a starting point. However, this will not cover the whole thing. For a quick check – you may do the following.
Observe D-9 Lagna
Look at the lagna lord in D-9. And planets placed in Lagna.
If these planets are in 8th house in D-1. A long-term illness is indicated.
Similarly, check the 8th lord and 8th house of D-9 chart.
If these planets are in Lagna of D-1, similar long-term illness is indicated.
Count houses from D-1 lagna to D-9 lagna
- If these are in 6/8 position, this is an add-on for severity. Please note, this point adds-up only if disease is confirmed using other combinations.
- If the lords of lagnas are mutual enemies, besides lagnas being in 6/8, this again adds-up. If they are friendly planets – will reduce the effect.
- Mere placement of Navams lagna and D-1 lagna in 6/8s will indicate a person who is working very hard in life / hustling in life with many jobs to do / responsibilities to fulfill. This can many times be good – since the native is pushing boundaries.
Observe D-9 Lagna
Look at the lagna lord in D-9. And planets placed in Lagna.
If these planets are in 6/12th house in D-1, constantly illnesses are bothering the person. 12th house may indicate diseases which cannot be diagnosed easily.
Similarly, check the 6/12th lords and planets in 6/12th house of D-9 chart.
If these planets are in Lagna of D-1, similar conditions as explained above are indicated.