The most common and most likely answer to this crossword clue is the 10 letter word HEATSTROKE
H
E
A
T
S
T
R
O
K
E
Buddy explains!
The straight part
We know that "serious medical problem" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case serious medical problem = heatstroke.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does HEATSTROKE mean?
HEATSTROKE noun- An illness caused by overheating a person or animal beyond its body's capacity to regulate internal temperature.