As far as the former is concerned, everything is obvious in this regard. In the year of the Dog, you are advised to 'grind away' less, and rest more. Of course, everything should be within reasonable limits, but a good holiday really wouldn't hurt, whereas working overtime, on the other hand, will be a source of problems, both in the family and in connection with your health. The result will be a malaise which will very quickly become a number of chronic illnesses which will be extremely hard to fight. But Mercury is on your side, and this means that by observing the basic rules of personal safety, you will be able to avoid all of this. You also need to be particularly careful with sharp objects, you could cause an injury. This doesn't concern Sagittarians whose profession involves a risk to their life as much as it concerns office workers, and there's actually nothing strange about such a trend.
The second semester of this period will be much calmer than the first, and it will once again bring certain adjustments into Sagittarians' lives. Nobody is likely to deliberately create a situation which can be characterized as a risk to your health. However, circumstances won't always be on your side, so you would do better to avoid going out into the cold without a cap, or running outside from the gym without cleaning yourself or drying yourself. A slight breeze could easily be enough to give you a cold, no immune system is safe from this, although Sagittarians are unlikely to have any difficulties with their immune systems in 2018. So pay attention more often not to yourself, but to your environment, because it could become a source of potential danger. Unfortunately, you will definitely face situations where someone from your household gets sick. During this time you would do best to stay far away from home, otherwise you'll also risk falling ill. Fortunately, this period is unlikely to last long, and aside from that, all of this will be a once off occurrence and not a trend.