Depending on the context, here are some possible alternatives:
If it means "very worrying":
* Troubling
* Distressing
* Alarming
* Concerning
* Anxiety-inducing
If it means "very bad":
* Dreadful
* Awful
* Horrible
* Appalling
* Terrible
If it means a combination of worrying and bad:
* Nightmarish
* Disastrous
* Catastrophic
* Heartbreaking
* Devastating
Ultimately, the best alternative will depend on the specific meaning you're trying to convey.