You've got to have a "Plan B"
If you can't remain upright because the suspect has grabbed your legs in such a way as to prevent you from sprawling, pull the suspect in, hold on tight and prepare for impact. Be sure to tuck your chin to your chest to prevent your head from slamming against the ground.
Immediately upon landing, wrap your legs around the suspect and cross your ankles, in what's commonly referred to as the "guard position." Apply pressure to the suspect's floating ribs by squeezing your legs together. This will not only inflict pain, but also tend to interfere with the suspect's breathing, both of which make it more difficult for him to hurt you. Pull his head down to mitigate his strikes. If he rises up to strike, protect your head with your hands and arms. Consider striking the suspect's eyes, throat, or using an improvised weapon.
If the suspect is choking you or attempting to disarm you, use whatever means necessary to establish control. If you can get to your pen, use it to strike the suspect's face or neck (sometimes the pen really is mightier than the sword). You could also use your pepper spray canister as an impact weapon, or even draw your firearm and shoot (bringing your firearm into play from the guard position can be difficult, especially if you've never practiced drawing from there. Additionally, retention is a primary concern when using your firearm while ground fighting).
If the suspect has taken you to the ground and continues to attack, his intentions are clear and your only choice is to respond immediately and aggressively.
Sprawling is a skill that should be in every officer's toolbox. Remember whenever possible, remain standing. If standing is not an option, land on top of the suspect. If you can't land on top, at least get to the guard position. From there, protect your head and transition to a more advantageous position at your earliest opportunity.
Train hard. Stay safe.