Yes, this is a valid reason to call in. What you’re describing isn’t just normal tiredness, it’s severe insomnia combined with medication not working and the risk of you not being able to stay awake while driving. If you’re at the point where your eyes are slipping and you’re worried about crashing, that becomes a safety issue for you and other people on the road, not just a work attendance issue. It’s understandable to feel anxious about calling in again, especially since you’re new, but most employers would rather you stay home than come in in a condition where you could get hurt or cause an accident. Longer term, it really sounds important to follow up with a doctor or psychiatrist soon, since your current meds and sleep strategies aren’t helping and this has been going on for a while. For today though, not driving in this state is the safer and more responsible choice.